HOW-TO: Replace Intake Air Temperature Sensor for LH Injection

[gerryvz]

Every 10-15 years, it is a prudent preventative maintenance item to replace the intake air temperature sensor. Located in the black plastic air scoop behind the driver's side headlight, the IAT sensor provides a key input to the LH injection system that meters fuel to the engine.

This IAT sensor is exposed to much of the incoming air and associated moisture, bugs and debris, etc. that is ingested into the driver's side "Zoom Tube" that leads to the air-box and air filters. Thus, it is bound to get degraded over time through surface corrosion, age and exposure to a broad variety of undesirable elements.

The time required for this job is approximately 10 minutes.

The job difficulty is a "2" on a scale of 1-10 (extremely easy).

Tools required for the job are:

• Medium to large size flat-blade screwdriver, or other prying lever
• Rag
• Quick detailer or other cleaning fluid

Part numbers required for the job are:

• Mercedes-Benz A 009 542 68 17 -- currently $19.50 list price, discounted to ~$14.00.

PROCEDURE:

First, release the hood of the vehicle from inside the cabin, driver's side, below the headlight switch. Open the hood at the front of the car.

Next, locate the black plastic air scoop panel behind the driver's side headlight, as shown below. The second photo shows the intake air temperature sensor plug, at the sensor location in the air scoop panel.



Then, remove the driver's side air intake ("zoom") tube and set it aside -- if your engine is hot, set it atop the fuse box/master cylinder area on the driver's side.



Unplug the two-pronged intake air temperature sensor plug by pulling it rearward, toward the ABS/ASR pump nearby.



After the IAT plug has been removed, pull the plastic air scoop panel directly upward to remove it from the engine compartment.



Bring the hood scoop panel over to a flat workbench, and lay it down, showing the inside of the panel as in the photos below. You can see the metal spring clip that holds the IAT sensor in position on the inside of the hood scoop.



Using your flat-blade screwdriver, carefully pry the clip off of the IAT sensor. Work each side of the clip with the end of the screwdriver blade, to ensure the clip is removed evenly from its bite on the IAT sensor's black plastic "wings."



This is what it looks like when the clip is released from the IAT sensor.



Turn the plastic air scoop panel upside down, and carefuly pull the IAT sensor out of its hole in the panel.



OPTIONAL: If you have a bench grinder with a wire wheel or sandpaper available, give the surface of the metal spring clip a few passes to clean it off.



Comparing the old (left) and new (right) intake air temperature sensors. Note the foam ring around the base of the new IAT -- there is a 100% guarantee that your foam ring on your IAT sensor is dilapidated and is 100% gone. The purpose of this foam ring is to eliminate air leakage around the sensor area.



Installation is pretty much the reverse of disassembly. Before you install the new IAT sensor, take a rag and some quick detailer spray, and thoroughly clean out the inside of the air scoop panel, focusing on removing the dirt around the area where the IAT sensor sits in the scoop.

Insert the IAT sensor into the hole in the outside of the air scoop panel.



Flip the intake air scoop panel over, holding the IAT sensor in place, and carefully begin pressing the spring clip into place under the little "wings" of the IAT sensor. Here are a few views of the clip partially and then fully installed underneath the IAT sensor.



After double-checking that the IAT sensor is securely held by the spring clip, re-install the air scoop behind the headlight and drop it into place. Plug in the connector to the new IAT sensor. Then re-install the zoom tube to the air scoop.



At this point you have completed the job.

 

[Jlaa]

Comparing the old (left) and new (right) intake air temperature sensors. Note the foam ring around the base of the new IAT -- there is a 100% guarantee that your foam ring on your IAT sensor is dilapidated and is 100% gone. The purpose of this foam ring is to eliminate air leakage around the sensor area.
View attachment 143266 View attachment 143267 View attachment 143268

Yep, my foam ring as totally gone as well.
And, my foam near the HVAC blower was ....... not in great shape.

I wonder where else foam lurks in the car that is now in terrible shape .... .... perhaps ignorance is bliss.

 

[gerryvz]

I wonder where else foam lurks in the car that is now in terrible shape .... .... perhaps ignorance is bliss.

Pieces that I found in my top-end refresh in 2020, included the foam that surrounds the plastic headlight buckets, as well as the blocky foam pieces that go UNDERNEATH the headlight buckets. All severely degraded, and replaced as part of my refresh.

Of course, none of these pieces are visible unless the headlights + buckets are removed, but they are there.

And @Jlaa, you and I both know that yours are degraded, and in strong need of replacement. Get on it !! Check my thread for reference if you need to.

 

[emerydc8]

 

[gerryvz]

Pieces that I found in my top-end refresh in 2020, included the foam that surrounds the plastic headlight buckets, as well as the blocky foam pieces that go UNDERNEATH the headlight buckets. All severely degraded, and replaced as part of my refresh.

Of course, none of these pieces are visible unless the headlights + buckets are removed, but they are there.

And @Jlaa, you and I both know that yours are degraded, and in strong need of replacement. Get on it !! Check my thread for reference if you need to.

@Jlaa -- Here's your foam HOW-TOs for the foam that you KNOW you NEED to replace due to degradation

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

Hi JC, Yes, I can get a socket on that remaining 13mm bolt that holds the bracket to the cylinder head, using a wobbly and a couple of long extensions. It seems that it is just a bit of an extreme angle with the wobbly, so I guess I'm going to have to find another shallower angle so that I can...

www.500eboard.co

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

:update: I'm at a point where I'm having to adjust the order of some of the tasks that I have been planning to do on the car, in addition to taking a hiatus for some of the Memorial Day holiday weekend, and this week. Specifically, I had intended to change the transmission fluid NOW, in...

www.500eboard.co

 

[Jlaa]

@Jlaa -- Here's your foam HOW-TOs for the foam that you KNOW you NEED to replace due to degradation

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

Hi JC, Yes, I can get a socket on that remaining 13mm bolt that holds the bracket to the cylinder head, using a wobbly and a couple of long extensions. It seems that it is just a bit of an extreme angle with the wobbly, so I guess I'm going to have to find another shallower angle so that I can...

www.500eboard.co

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

:update: I'm at a point where I'm having to adjust the order of some of the tasks that I have been planning to do on the car, in addition to taking a hiatus for some of the Memorial Day holiday weekend, and this week. Specifically, I had intended to change the transmission fluid NOW, in...

www.500eboard.co

I am tackling various fixit opportunities on my sport beetle. I showered the 500E with lots of maintenance over the past some years, so I am now reciprocating to my sport beetle now.

In other words, I am procrastinating. I spent so much effort chasing and fixing vibes that I need to enjoy the car for a while before giving myself high blood pressure by tackling another fixit job which will invariably result in me breaking something.

 

[gerryvz]

Meanwhile, ozone & exposure continue to degrade the foam further. It’s easy to envision little grains and cells flaking off with wind pressure as the car is driven.

Degrading, eroding,,,, a deferred maintenance time Bomb going tick, tick, tick ….

 

[emerydc8]

 

[Eno]

Just curious what are the symptoms on the car if this sensor is missing at all?

 

[gerryvz]

There are several symptoms reported by forum members that are detailed in various other threads if you search "intake air temp sensor". This is primarily a HOW-TO thread on replacement.

 

[TerryA]

Just curious what are the symptoms on the car if this sensor is missing at all?

When mine was bad the CEL was on. The part was $10.00 at the time.

 

[gsxr]

Terry is correct, if the IAT is disconnected or defective, it will trigger a CEL almost immediately. However, only North American models have the CEL. Symptoms otherwise would be a very slight reduction in power that most people wouldn't notice, along with fault code #13 stored on pin 4 / LH.

 

[gcstein]

Terry is correct, if the IAT is disconnected or defective, it will trigger a CEL almost immediately. However, only North American models have the CEL. Symptoms otherwise would be a very slight reduction in power that most people wouldn't notice, along with fault code #13 stored on pin 4 / LH.

Hey, I've got a very slight reduction in power that I don't notice!

 

[Sam SL]

I went to replace the sensor today only to find the old one connected but dangling on its connector and not inserted through the opening of the headlight cover. It appears the spring clip is missing all together. Now this all makes sense because through the years and the all the times I went to remove the driver's headlight cover I never noticed anything attached to the cover. Today I finally notice the hole!

Went to order the clip. It's $24 even with the discount. That's shocking.

 

[TerryA]

@Sam SL, Geez, I only paid $10 for the sensor but I didn’t need the clip.

FYI, I paid MB of Long Beach about $100.00 to find out what triggered the . Guido/ aka Italian Benz on 500Ectasy was a tech there and checked my 500E out. I knew him because I almost bought his 500E. The Dealership wanted the $100.00, Guido would have done it for nothing.

 

[nocfn]

There should be a way to close that loop and put away the sensor altogether when it becomes NLA or cost prohibitive. Maybe you circuit junkies (@JLA comes to mind) can research it so we can stop the madness for future use.