EGR fault

[J. M. van Swaay]

1994 E500, 115K miles

CEL on
pin 4 code 16, EGR switchover valve
pin 19 code 5, EGR inop

verified vac lines to and from switchover valve, verified function of switchover valve, engine stumbles when vac (mighty vac) applied to EGR during idle, resumes normal idle when vac released.

cleared codes but they returned...

removed EGR valve to roto root passages with speedo cable.

Question, there are two passages to/from the egr valve. One has a slanted entry and goes to the drivers side, over goes to passenger side. If my problem is a coked over orifice somewhere on which side is it likely to be? Also, anybody know what length of speedo cable must be inserted to clear a possible obstruction?

Any other suggestions would of course be appreciated.

Thanks,

J. M. Van Swaay

 

[gsxr]

JM, code 16 on pin 4 indicates an electrical issue, meaning the LH module signal to trigger the EGR vac solenoid is either open or shorted. Check the electrical circuit.

Code 5 on pin 19 is causing the CEL, and indicates that the EGR valve is not opening, but doesn't indicate why. Pin 4 / code 16 is telling you why.

Your test of applying vacuum to the EGR was good, since the engine stumbles during the test, it confirms both the EGR valve is working *and* the orifices are clean.

 

[J. M. van Swaay]

Hi Dave, I wasn’t sure how the two codes were related, thanks for the clarification. I did remove the switchover valve from the front right fender wall to check it. When I applied 12vdc to the terminals, I could hear and feel a click, and the vac ports switched like they are supposed to. I believe the normal not energized state ports the egr valve to atmosphere and the energized state ports the egr valve to manifold vacuum As you know, there is a vac line that goes from the intake manifold to the area on the right front fender wall, I believe it also serves to supply vac for the smog pump activation. Is that correct? There is a one way check valve between those two valves there on the fender wall, is it possible that if it were stuck open that it could trigger the codes I’m getting?

I did a quick check of the wiring to the switchover valve and all appears normal but I can’t really trace the wires from the valve to the ecu...

Thanks again for the help!

 

[gsxr]

JM, your understanding is exactly correct!

If it were a vacuum issue, you'd have code 5 on pin 19, but probably *not* code 16 on pin 4. However it would still be a good idea to verify all the vacuum plumbing is intact.

Unfortunately at this point, it's difficult to diagnose further without a digital scanner / SDS, where you can manually activate the EGR from the scanner with the engine running, to confirm that a +12v signal is present at the switchover valve. And when the system is working normally, this activation will make the engine stumble at idle.

 

[J. M. van Swaay]

Update:

After clearing the same recurring codes a few more times, I decided on “diagnosis by part replacement”. Not really a process I like but any additional diagnosis would have required a commercial service visit probably at a cost of a few hundred dollars. I took a chance and replaced the switchover valve and the vacuum check valve — $40 in parts and about 30 minutes of my labor. So far after about 20 drive cycles the codes have not returned. Think I’ll claim a victory....

Thanks again for the expertise on this board.

J. M. van Swaay