Seeking Beginner DTC Advice, 1995 E420, No ASR

[luckymike]

Folks,

I'm really frustrated by my lacking knowledge of the LH system. I enjoy tinkering with the CIS-E system on our 126s but am aggravated by our E420. I guess it's more a feeling of helplessness since I won't turn the car over to a mechanic.

Okay, that admitted, I seek next-step advice. I know the codes but really don't know how to proceed. Car is a 1995 E420, no ASR. It starts and runs adequately but is not silky smooth as it should be. It is very stinky and won't pass smog. The idle fluctuates between 900 and 1400 or something. It struggles and bucks when attempting full throttle. Correct new plugs. Caps, rotors and insulators are new. No change between before and after installation of these parts.

Per my blink code reader, I have the following:

Pin 4: Code 10 returns. If I understand our official DTC Code .pdf, this means there is a problem with the cruise control module N4/3. I don't understand the "Test step/Remedy" 23 => 15.0

Pin 7: Code 2 returns. Without the additional 3-digit codes provided by a better code reader, there are a number of possibilities here. Several point to the cruise control.

Pin 19: Code 6 returns. Idle speed control inoperative. "Test electronic accelerator section 6.2" ??

So I guess I need to investigate the CC module and maybe the ETA? FYI, I rewired my own ETA (see here ETA Rewiring | 400E / E420 Discussions) and it worked fine for a long time.

I would love it if someone has been here before and can tell me to "just replace the CC module and you'll be good to go".

Any other guidance?

 

[gsxr]

Sounds like you need to view live data, not just fault codes. You can get a basic idea of what may be wrong with codes, but live data takes it to a whole new level. That said, for really difficult (or intermittent) problems, even live data won't pinpoint the root cause right away.

Anyway:

LH code 10 is: "CTP (idle) recognition from ... CC/ISC [T/LLR] control module (N4/3), short circuit". "Test step/Remedy" 23 => 15.0 is indicating the location of further troubleshooting steps in Diagnostic Manual, available both online or in the WIS. If you have a different T/LLR and/or LH module, swap them and see if the same code keeps returning. If so, might be a wiring issue, or a faulty ETA>

T/LLR code 2 is difficult, as you noted, without a digital scanner (which would also show live data). But it's mostly pointing to the ETA or related items. Since there are no other codes, it isn't likely to be the stop lamp switch which would trigger another code. Remmeber that CC/ISC is Cruise Control / Idle Speed Control module T/LLR. This has nothing to do with cruise control, although if cruise control is not working, this points back to a faulty ETA or T/LLR module as possibilities.

DM code 6: This is just telling you there's a problem with the T/LLR and/or ETA, which you already know because it won't idle at normal RPM. Test section 6.2 is part of the diagnostic manuals.

Also remember there is not a separate cruise control module under the steering column, as on non-V8 cars. This function is in the T/LLR module, and the cruise actuator is replaced by the ETA.


Diagnostic Manuals:
http://manual.startekinfo.com/manual/JSP/sitemap.jsp

LH injection for M119, note section 23/1...
http://manual.startekinfo.com/manual/JSP/e2/3_1/content.jsp

LH injection for M119, section 23, step 15.0:
http://manual.startekinfo.com/manual/JSP/e2/3_1/m23.jsp

Problem here is the manuals assume you have a special breakout box that lets you measure voltage on every pin on the LH module, which you won't have (nobody does, even many dealers won't have those).

DM test section 6.2 link:
http://manual.startekinfo.com/manual/JSP/e3/6_2/content.jsp

 

[gerryvz]

Before we get into the discussion .... first of all, have you replaced both your upper (especially your upper) and lower wiring harnesses?

LH is MUCH MUCH easier and less finicky to deal with than CIS-E. And I own and love both (actually I love CIS-E more). LH is more instrumented and thus easier to diagnose issues with.

The codes you are quoting are pointing to my estimation, to the throttle body. Even as a matter of course, I would send yours down to Don Roden in Alabama and get it repaired/rewired on the inside and outside. It's not just the wiring that goes bad with these units (the external and internal wiring). The potentiometers and gears inside ALSO go bad with age and use.

My E500 was running perfectly, ZERO issues with my ETA (original). I sent it to Don Roden for a rebuild. He found a couple of issues with it on the inside; it was not working 100% correctly. And this was not even anything to do with the wiring, which was bad and probably was completely shot when I disturbed it in the process of removing it. Don sent me back a section of the wiring, which I posted photos of in my Project Journal article I did this spring/summer on the M119 top end rebuild.

The non-ASR cars don't have an EA, just CC/ISC (cruise control / idle speed control) and are not (if I remember correctly) "drive by wire" cars like the ASR cars are. The non-ASR cars have a direct mechanical connection to the throttle body.

On the LH module (pin 4), your code 10 is saying that there is an idle signal anomaly. For the resolution step, you will need the WIS to determine that.

For Pin 7, the CC/ISC module, you are defintely going to need a 3-digit-capable reader to further pinpoint the code. High likelihood that it is inter-related with your Pin #4 code 10, though. As you can see, it can be a wide range of things. Is there any way you can get a 3-digit capable reader, or bring the car to someone who has one? Perhaps one of our members in the area, like @RicardoD, or someone like that?

Pin 19, your DM (which controls the CEL) is a direct EA code.

All three of these issues above are caused by the EA. So that is where I would start. Not sure if you have a spare, but that is one option, testing with a known-good spare. Otherwise, spend the $350-400 and have Don work yours over (or exchange it with one he has rebuilt on his shelf).

 

[gsxr]

Car is a 1995 E420, no ASR. It starts and runs adequately but is not silky smooth as it should be. It is very stinky and won't pass smog. The idle fluctuates between 900 and 1400 or something. It struggles and bucks when attempting full throttle. Correct new plugs. Caps, rotors and insulators are new. No change between before and after installation of these parts.

Any other guidance?

Test 1: Disconnect the MAF, go for a test drive. See if the power is normal at full throttle. If it runs better, your MAF may be faulty. If there's no change at all, the MAF may be ok. Only way to confirm a good MAF is viewing live data though.

Test 2: Remove the exhaust crossover pipe, go for a (loud) test drive. See if the power is normal at full throttle. If so, your catalysts are plugged. Stinky exhaust is a clue here. You can also temporarily plumb in an exhaust backpressure gauge before the cats, if you have one, and view the pressure while driving (can't test in the driveway, revving the engine with no load usually won't show anything unless the exhaust is drastically blocked).

AFAICT... the idle speed issue is separate. Just having faulty idle speed control (ISC) should not limit full throttle power or cause bucking.

Can you post the smog test results?

 

[luckymike]

Wonderful! Thanks, guys.

Upper harness has been replaced prior to my ownership. Lower is an unknown.

I'm willing and ready to send my ETA to Don Roden, just don't want to do it prematurely.

I know at least one local guy who might be able to help me with more detailed codes.

The 'won't pass smog' comment was actually an assumption on my part. CEL is on and with the stinky exhaust I assume it won't pass. If the test results would be helpful here at the beginning, I will have that done. Please let me know if this could wait or if I should have the car tested now.

I'll start simple and swap in my spare LH and T/LLR modules and also do the no-MAF test and report back.

Thank you, again.

 

[gsxr]

Nah, don't bother with the emissions test... see if you can get it running better first. Shouldn't be any funky smells out the tailpipe. That indicates bad cats, rich mixture, or incomplete combustion (misfiring), or some combination of the above.

Definitely swap modules around first, and try the MAF disconnect. That should start ruling out a few possibilities.

 

[Kyiv]

How about one of the two coils being bad?

 

[luckymike]

How about one of the two coils being bad?

Interesting. That would be fantastic. I'll look up how to test unless someone has it already.

I don't have access to a scope.

 

[Kyiv]

Bosch coils are $70-75 on FCPeuro. If they have never been replaced, I think they should be on principle. When my 400E developed a fluctuating idle, unburned fuel smell, buckled and struggled at full throttle it was due to one of the original coils being bad. This may not be your case, but, since caps, rotors, and insulators are new, coils are the next "baseline" item. They are easy to replace too

 

[gsxr]

This is where live data can be helpful, as the SDS will show ignition voltages for each cylinder. If one cap/rotor/coil is flaky, you will usually be able to see it in the data, and it also pinpoints ignition as the root cause. But anyway, yes, original coils are suspect after 25 years, especially with higher miles. Tip: Pull the driver headlight and make the coil replacement job a breeze. It's miserable if you don't pull the headlight.

If there is no change in symptoms after replacing the coils... and the issue still appears to be mixture related (strong exhaust odor, poor power, poor throttle response, erratic idle, etc)... I'd consider replacing the crank sensor if it's not recent, and despite there being no fault code. Someone else went through a similar scenario and replaced almost everything you can imagine, and it ended up being a dying CKP. In that case live data was showing abnormal lambda control values.

 

[gerryvz]

If you do replace the coils, “while you are in there” you should also inspect and replace the blower motor resistor, which is located next to the coils. This is a part that gradually corrodes and goes bad. It’s only available from MB these days, but at a minimum you should inspect it visually.

 

[luckymike]

Bosch coils are $70-75 on FCPeuro. If they have never been replaced, I think they should be on principle. When my 400E developed a fluctuating idle, unburned fuel smell, buckled and struggled at full throttle it was due to one of the original coils being bad. This may not be your case, but, since caps, rotors, and insulators are new, coils are the next "baseline" item. They are easy to replace too

I like this idea, kiev. Thanks. Not a huge cash outlay and likely needed anyway. And thanks for the FCPeuro tip.

Gerry, I remember working on some kind of a resistor in the area you're talking about but this was for the radiator fans. Is that the one you're referring to? Do you have a part number handy?

 

[gsxr]

Yep, it's the resistor for the auxiliary cooling fans ahead of the condenser. Details here:

Difficulty finding Aux Fan Resistor | Heating and Cooling (Interior HVAC systems)

Recently my aux fan resistor began overheating. I attempted to locate a replacement online with the usual suspects. I have been unable to procure one. ECS Tuning showed a BEHR resistor which I ordered, but after a week and no updates on shipping they offered me a Mercedes part. My dealer...

www.500eboard.co

 

[gerryvz]

Yeah, I meant the aux fan resistor. Part number: 000 158 32 45 MB Annapolis part price $33.60.

I replaced it here: RESTO PROJECT: M119 / W124 / E500 Engine Top-End Refresh | Member Roadtrips and Project Journals

Old and new: RESTO PROJECT: M119 / W124 / E500 Engine Top-End Refresh | Member Roadtrips and Project Journals

 

[luckymike]

Well, that's just PEACHY. The poor running wasn't enough so the car suddenly decided to not start. Turns out if you wiggle your crankshaft position sensor just the right way, your car will start.

UPDATE: T/LLR module swap made no difference in the running. Still need to do MAF disconnect now that the car is running again. Getting ready to order coils.

 

[gerryvz]

Spend the $35 and get a replacement resistor, too.

 

[luckymike]

UPDATE:

MAF disconnect, no change. LH module swap, no change. New CPS, car starts consistently but that isn't the purpose of this thread. Two new Bosch coils, no change, though full throttle seems improved.

Caps, rotors and insulators are new. Idle is always high but sometimes fluctuates between 1000 and 1200. It will just sit there going up and down, up and down. Cruise control does not work. Exhaust is stinky.

I believe the next step is to have Don Roden rebuild the ETA. Do you all agree?

 

[gsxr]

If the primary remaining symptom is the high/fluctuating idle, then yes, I would have Don rebuild the ETA.

The only thing that is odd, is the stinky exhaust. That is a mixture problem, not throttle control. Not sure what's going on there.

It will be VERY hard to pinpoint further without live data from SDS/HHT-Win, for either the idle RPM issue, or mixture issue.

 

[luckymike]

Okay. I'll talk to Don next week and get that in the works.

The car is stinky at idle but since it runs so great otherwise, I figured it was a mixture thing only at idle. Obviously I have no real idea. I'll just start with the ETA and go from there.

Thanks for the nudge, gsxr.

 

[Ascension]

Sounds like you have a bad ETA. I have a 95 E 420 that is a non ASR car and am about to replace the ETA a second time on my car, it is showing the exact same symptoms with cruse inop and the idle yours is. Roden is just a few miles from me so will get Dan to build me a new one or may just drive up and drop it with him and let him run full diagnostics. Don't think the smell is the ETA though. A bad vacuum leak can cause both issues have run smoke?

 

[luckymike]

I have not done a smoke test but the car runs wonderfully off idle.

Second time ETA replacement?! Not a Roden issue, I hope...

 

[luckymike]

UPDATE:

ETA sent off to Don Roden today.

 

[Ascension]

I have not done a smoke test but the car runs wonderfully off idle.

Second time ETA replacement?! Not a Roden issue, I hope...

No original was eco junk wiring and after moving that harnes knew it would fail. Was replaced with a used ETA as Roden was not around then.

 

[luckymike]

Well, this is stupid. Took the car out for a five-minute drive to post office and turned it off. Came out to a car that would crank and pop but not start.

History: As part of the troubleshooting in this post, I had reinstalled my old LH full throttle module. It had been removed because it was clicking (fuel pumps). The car started and ran fine but on this morning, there was some stumble at stop lights and then the no start.

I had left the current LH module in the trunk with the tools to replace it so I put it back in. Car fired right up.

Fast forward a few days. Take the car for a short drive, two miles, turn it off for 10 minutes. Come out, won't start. Crank, crank, crank, loud popping out the exhaust. With the original, current LH module installed! And a brand new crank position sensor! Aaaargh. Let cool, car starts.

I welcome any input. Talked to Don Roden this morning and the ETA is on it's way back. I'm crossing my fingers that the ETA is the answer to all my problems.

 

[gsxr]

For grins, when it acts up, measure resistance of the crank sensor.

I'm also hoping the ETA may help, but a bad ETA generally shouldn't prevent starting.

BTW, what's the current rate for Don? I'm seeing $400 on eBay now, ouch. Wasn't sure if he had lower prices if you dealt with him directly.

 

[luckymike]

Ugh. Yes, I'll check the CPS resistance.

Current Don rate is $379 which includes return shipping. One side of me balks at the cost and the other says, if this fixes my issues it's TOTALLY worth it. Hope to install this weekend.

 

[gsxr]

Current Don rate is $379 which includes return shipping. One side of me balks at the cost and the other says, if this fixes my issues it's TOTALLY worth it. Hope to install this weekend.

I think it's totally worth it either way. Once-per-ownership expense, 3-year warranty, but should last the lifetime of the car. I mean, even @Glen 's high-miler wasn't eating ETA's every 200k. Probably changed once, maybe twice? Glen, were there any record from @DrP ?

At least you can rule out the ETA once it's back on with the linkage adjusted correctly.

 

[Glen]

I'd have to verify but I think it may have been changed once.

 

[a777fan]

Mike, my hot no start condition (with intake backfiring (the popping you mention)) was traced back to faulty rotors. How do yours look? Have you checked their resistance against the spec in the diagnostic manual?

Sad to say mine that failed were a little over two years old, and were OE. i have theorys on why, but nothing I can prove. Replacing them solved my issues.

 

[luckymike]

Mike, my hot no start condition (with intake backfiring (the popping you mention)) was traced back to faulty rotors. How do yours look? Have you checked their resistance against the spec in the diagnostic manual?

Sad to say mine that failed were a little over two years old, and were OE. i have theorys on why, but nothing I can prove. Replacing them solved my issues.

a777fan, caps and rotors have 20,000 miles on them, insulators about 2,000. But I'll be removing and inspecting both when I install the new ETA. Thanks for the input.

Oh, no I haven't checked resistance.

 

[gerryvz]

Cap and rotor replacement and/or inspection is 100% useless without also replacing the insulators behind them.

Even insulators that “appear” fine are in dire need of replacement. I can’t tell you the number of times on this forum that people have replaced their caps and rotors (or had a shop do it) and they didn’t bother to take care of the actual culprit.....which are the plastic insulators between the cylinder head cover and the cap/rotor.

 

[gsxr]

...but he replaced insulators 2kmi ago.

 

[gsxr]

a777fan, caps and rotors have 20,000 miles on them, insulators about 2,000. But I'll be removing and inspecting both when I install the new ETA.

Any news since the new ETA has been installed?

 

[luckymike]

Any news since the new ETA has been installed?

YES! And yes... I just need a minute to settle down from all that's going on and I'll post an update.

 

[Kyiv]

YES! And yes... I just need a minute to settle down from all that's going on and I'll post an update.

Hurry up! We want to know if we can open the

 

[Jlaa]

C’mon it has been over TWENTY-FIVE THOUSAND SECONDS after needing “a minute to settle down.” Can we celebrate?

 

[luckymike]

You guys are cracking me up! I'll commit to writing a post tomorrow. It's not all good news. We're a lot closer but not there yet. Something interesting about the used distributor caps I had to install...

 

[nocfn]

Are they Yurro?

 

[luckymike]

UPDATE:

Thank you all for waiting. Anyone else caring for an aging parent? Man, what a job.

I sent my ETA off to Don Roden on a Thursday and got it back the next Thursday. $379 included shipping. It arrived VERY well packed with complete paperwork showing a checklist including a test drive. Yes, he installs every ETA on a car and drives it. Impressive. And it comes with a gasket installed.

Before installing the ETA, I cleared all the codes. I installed it and per Don, turned the key to run and waited for two minutes. The check engine light was on and he said it would blink and turn off after a couple minutes. It never blinked but it did turn off. I was so apprehensive about the whole process! There was so much riding on this rebuilt ETA.

After the CEL went out, I turned off the key and then started the car. For the first time in forever, the engine jumped to a fast idle and quickly settled down to a nice, low idle. I was thrilled! Until a few seconds after that, the car started running rough. Great. With this bad news, I was ready to button everything up and return to fight another day, I needed to get to Mom's to relieve my wife. Then I remembered i was going to check the caps and rotors during today's festivities.

I quickly pulled off the passenger side cap and was very surprised to see not one but possibly two dark cracks from plug terminals to the center electrode. What?? How could this happen right after installing the ETA? The car had run smoothly as I drove it over to the shop. My theory is that the high idle of the ETA before rebuilding was masking the cap-induced missing. These caps and rotors were Bremi.

At any rate, I pulled my old Bosch caps out of the trunk. I had put them in a plastic bag long ago after installing the Bremis and forgotten about them until now. Imagine my surprise to pull them out and discover the telltale moisture that we all deal with, inside these old caps. I did not put them in the bag wet. My theory is the moisture had to come from inside the plastic somehow. Nothing else inside the ziploc bag had any moisture on it. Just the interior of the old caps.

Installed the passenger Bosch cap, car ran noticeably smoother. Installed the old Bosch rotor, better still. Pulled the driver's side cap. Another crack and some apparent tracking. Very disappointing but also exciting. Installed the driver's side used Bosch cap, running even better. For a reason I no longer remember, I didn't have the old Bosch rotor. Checked both insulators. Still good but then they only have a couple thousand miles on them.

At this point I drove home. Car ran well (and the cruise control is back!) but stumbled at stop lights in drive. Better in neutral.

Didn't drive the car again until yesterday morning, about a week later. Car fires right up and settles into a nice, low idle. But intermittently stumbles. And a couple times when accelerating just a little more than normal driving, the car would fall flat on it's face. If it had ASR, I'd say it felt like I imagine limp home mode to feel. Backed off the pedal and car could accelerate slowly. This symptom is completely new and intermittent.

One more thing. I finally got around to replacing the six capacitors in the LH module (the one with the higher full throttle horsepower) that came with the car. I had to swap it out years ago because it was causing the fuel pump relay under the back seat to click. My correct year substitute has been in the car since.

THE PLAN: I think it's premature to ask for advice just yet. My plan is to get new Bosch caps and rotors installed and see how that goes. Depending on the outcome, I'll reinstall the repaired (hopefully) LH module and see what effect that has. I'll post again after I reach that point.

I'm thrilled with the improvement so far, even though it's not perfect yet. I'm tempted to give the smog test a try because I don't think the exhaust is stinky anymore, which is the reason I was forced to get into all this.

Sincere thanks to all who have chimed in with advice.

 

[gsxr]

I quickly pulled off the passenger side cap and was very surprised to see not one but possibly two dark cracks from plug terminals to the center electrode. ... These caps and rotors were Bremi.

Can you post photos? Are there cracks in the plastic, or just black carbon tracks from misfiring? This isn't helping my already low opinion of Bremi. You may want to buy new caps/rotors from FCP as the lifetime warranty may be quite useful...

Didn't drive the car again until yesterday morning, about a week later. Car fires right up and settles into a nice, low idle. But intermittently stumbles.

Is the intermittent stumble after a cold start, during the warmup phase?

And a couple times when accelerating just a little more than normal driving, the car would fall flat on it's face. If it had ASR, I'd say it felt like I imagine limp home mode to feel. Backed off the pedal and car could accelerate slowly. This symptom is completely new and intermittent.

When this occurs, is it a smooth power loss (no misfiring), or does it feel like a misfire / roughness when you push the pedal down and the car doesn't want to accelerate?

I'm thrilled with the improvement so far, even though it's not perfect yet. I'm tempted to give the smog test a try because I don't think the exhaust is stinky anymore, which is the reason I was forced to get into all this.

The exhaust stink was likely from the misfiring / bad caps. I wouldn't get a smog test until you get the idle stumble fixed, assuming your local emissions test includes idle testing.

 

[luckymike]

1. Can you post photos? Are there cracks in the plastic, or just black carbon tracks from misfiring? This isn't helping my already low opinion of Bremi. You may want to buy new caps/rotors from FCP as the lifetime warranty may be quite useful...

Yes, I will do this.

2. Is the intermittent stumble after a cold start, during the warmup phase?

Still figuring this out.

3. When this occurs, is it a smooth power loss (no misfiring), or does it feel like a misfire / roughness when you push the pedal down and the car doesn't want to accelerate?

It's like a light switch. Pushing the pedal to a certain point causes the engine to fall flat on its face. And not until I back off to a certain point does it recover. I guess given those two choices, I'd say it's a smooth loss. But it's certainly not gradual. It's immediate at that certain pedal depth. Definitely not a misfire or roughness. It's like someone turned a dimmer switch down suddenly.

4. The exhaust stink was likely from the misfiring / bad caps. I wouldn't get a smog test until you get the idle stumble fixed, assuming your local emissions test includes idle testing.

Agreed. FCP order placed.

 

[gsxr]

Just curious - are the fuel pumps old/original?

 

[luckymike]

One is original, one is a used replacement I installed from another car. I've actually wondered about this, as well. Pressure dropping under the pressure of demand?

 

[gsxr]

A failing fuel pump can cause a smooth loss of power under load, that feels like you are giving it 10% throttle, regardless of throttle position. The car may idle and rev normally in the driveway, and when driving the problem can be intermittent. I had one car years ago give me fits diagnosing this symptom, I finally pinpointed it with a remote fuel pressure gauge I could watch while driving. New Bosch pumps cured it permanently. I later had another car with the same issue, same diagnostics used, same resolution.

Side note: You can test used pumps before installing. IIRC, current draw should be <1 amp and the pump should be fairly quiet. If current draw is much higher (say, 1.5-2.0 or more), or sounds like it's full of marbles, it shouldn't be put back into service. I've also found that used pumps may leak slightly for a brief period after being put back into service, after sitting on the shelf for months or years. I've kind of given up on used pumps for any cars I need to be reliable...

 

[luckymike]

Here are the promised pics. Not sure how much they show thanks to a poor quality camera. Not sure why the gray tracking lines disappeared. The arrows point to them.

Interesting is that the moisture pattern forms a sort of roundish star pattern around the plug terminals. Cap is dry between the terminals.

Received the rotors from FCP, awaiting caps next week.

Car seems to slowly be improving. I'm not going to worry too much until the new caps and rotors are in.

 

[gerryvz]

Per my post 31 above which you did not reply to …. you also did order new insulators to go with the new caps and motors? It’s futile not to replace the insulators at the same time. Not joking.

I know you said you visually checked yours and they are newish. I would baseline with new ones at the same time as caps and rotors.

 

[luckymike]

I like the idea of getting a baseline, even though the current insulators only have 2,000 miles on them.

I'm determined to get this car running as it should, but at another $110 or so for insulators, I'll try the caps and rotors first.

 

[gsxr]

If the insulators are only 2000 miles old, they should be fine. I think Gerry was questioning if they were original. (?) I don't think the Bremi bits can "damage" fresh insulators.

 

[luckymike]

UPDATE TEASER.

New Bosch caps and rotors from FCPeuro went in today. That's the good news. Fired right up. Unfortunately I can't do a full test drive for at least a week. Stay tuned.

Bowden cable passed the friction test but failed the vacuum. So I assume my upshift delay isn't working and even if everything else IS okay, WON'T work until this part is replaced. Correct?

Valve body springs check will have to wait for now.

 

[gsxr]

Bowden cable passed the friction test but failed the vacuum. So I assume my upshift delay isn't working and even if everything else IS okay, WON'T work until this part is replaced. Correct?

Correct. If it fails the vacuum test, you will not get any cold upshift delay. But if there's no CEL, I wouldn't worry about it. Consider that a "feature".