My check engine light came on and I am coming up with code 26. It usually comes on when I come to an idle position from normal speed. It states that it has something to do with a quad control module. Anyone know where this is? Is it part of the PCM? Thank you!

 

Code 26 is a "quad output driver fault".

Several different devices/sensors share a portion of the PCM's functionality; if any one of these devices misbehaves, it can trigger a code 26. Note that in general, it is almost never the PCM itself that has a problem -- it is one of the devices or sensors tied into this circuit that is throwing the code.

Things normally on this circuit for the S cars are
1) SES light itself
2) Coolant Hot (idiot) dash light
3) aux coolant fan relay
4) A/C clutch relay
5) speedometer cutout circuit
6) Upshift dash light / Shift to D2 light (Man/Auto trans, resp)
7) EGR Solenoid
8) CCP solenoid (charcoal canister purge)

Check the above in the order listed.

Based on your description of when the code is thrown and your lack of any other described symptoms, I would tend to think it is the EGR solenoid, since the EGR solenoid is the only device above whose behavior/operation is clearly engine-speed dependent (CCP may also be but not sure).

Aux Coolant fan relays also go bad.....but I wouldn't expect this to show up as an engine-speed related phenomenon.

Please post resolution

Derf

 

Thanks for the info. I will it a shot. If I was to guess, I would look at the speedometer cutout circuit because the check engine light always goes off when I reach about 30 MPH and comes back on when I come to a stop and idle position.

 

If your speedo works properly (sounds like it does) , then I don't believe it can be your speedo cutout circuitry......

Based on SES behavior you described in your followup, it seems that the SES goes out after you've finished heavy acceleration, and the EGR is problably sitting partially open while cruising. When you decel back to idle, the EGR solenoid is probably trying to get the EGR to close but the solenoid is probably stuck in the engaged position and therefore can't respond.

Does this car run rough or have gyrations in the rpms when decel'ing??

What happens to the SES when you slowly run the revs slowly up to about 3k and then slowly back to idle while the car is in neutral?

btw, what year/model is this car?


Derf

 

Sorry. I have been have been out of town. The car is a 92 SL2, dual overhead cam/manual transmission. I have tried the revs in neutral and the light stays on. It only goes off when I am in motion at about 30 to 40mph. I still have to check all those circuits you told me about. Thanks.