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Hey Everyone,
I am looking for help solving/ diagnosing my Quad Driver Module code 26 on my 1992. This code doesn't seem to be affecting drivability at all but it is a check engine light that I want to take care of.
I have a Tech 2 clone I am using to help with diagnostics along with the code 26 chart from the FSM.
The code chart wants to verify activation of the Air Pump Relay, Air Solenoid, EGR Solenoid and Canister Purge Solenoid (See pic of code chart)
On the Tech 2 I see EVAP Purge Solenoid, EGR Solenoid and Air System. When I activate them with the scan tool this is what I hear/ feel happening under the hood.. (See labeled underhood pic.) I made the pic big so that anyone might be able to point to other components or areas I need to take a look at.
Can anyone give any further guidance on how to proceed?
The Quad Drivers (QD) activate various relays and solenoids (Up to 4 each, hence the "quad".). The relay coils have +12V on one side, the other side is grounded by the QD. When the circuit is not activated, the level at the quad driver output will be high, or 12 Volts. When the circuit is activated, the level at the output will be Low, or 0 Volts. The ECM monitors the outputs and states of the QD, and if an output is not in the state that it is commanded to be in, ie an output is Low, but it is commanded Off so it should be High, the Code will set.
My experience has been that Quad Driver Codes are set by poor connections or removed components. Or possibly a bad relay coil, but this is rare.
If you have the wiring diagram, this is how I test: Key = OFF. Unplug all the connectors from the ECM. Identify and locate the connector and cavity for the four circuits controlled by QD1. Turn key to RUN. Check each QD controlled circuit for the presence of 12 Volts. If any are 0-Volt, check that relay and connections. Ground each circuit. That relay or solenoid should click and function. Note: The QD codes only monitor the electrical integrity of these solenoids and relays. Not the function itself. Ie, if a solenoid plunger is stuck, or the vacuum hose is split, that controlled system won't function, but the electrical response that the QD is monitored for is still nominal. So the QD code won't set.
My book for 1992 shows A1 = Canister Purge, A2 = EGR, A7 = A.I.R. Relay, and A8 = ESV Solenoid. Connector A is Gray.
EDIT/ ADD: Note: In your picture, "AIR SYSTEM" is actually the ESV (Air Switching Valve). The A.I.R. Relay is attached to the AIR pump in the lower right of the picture, adjacent to the vacuum ball. I can see it's connector just poking out to the right of the hood support.
Thanks for taking the time to respond with such a thorough answer. Tomorrow I will head out to the garage and follow your instructions. Thanks for clarifying the AIR SYSTEM is ESV, I'm a little disappointed the AIR Relay isn't controllable by the TECH 2 scan tool. But your method should guide me towards a solution.
Thank you,
Dennis
Key = OFF. Unplug all the connectors from the ECM. Identify and locate the connector and cavity for the four circuits controlled by QD1. Turn key to RUN. Check each QD controlled circuit for the presence of 12 Volts. If any are 0-Volt, check that relay and connections. Ground each circuit. That relay or solenoid should click and function.
My book for 1992 shows A1 = Canister Purge, A2 = EGR, A7 = A.I.R. Relay, and A8 = ESV Solenoid. Connector A is Gray.
So I followed these directions and am now starting to suspect my ECM which sucks cause this is a 92.
I am able to confirm with key on engine off, 12v at all 4 pins.
I then grounded them and can confirm all solenoids/ relays function properly.
Any further steps I can check before going on the search for a ECM or sending it out for repair?
I used SIA as well on my original 93 ECM. They reflowed it. Seemed to work for a few months and then went poof seemingly. I bought a used 92 repaired one and swapped my prom chip. Car runs flawless again and I actually hear my door chime for the first time. I think the SIA reflow had a short or component fail. I’ll be sending it back under warrantee to hopefully be fixed as a back up.
I had the quad driver circuit codes when my ECM crapped out. SIA fixed it many years ago.
I just confirmed the ECM is causing the QDM Code 26.
My service engine light comes on consistently, every time I drive it. Sometimes a minute in sometimes a few minutes but I know it will come on every time.
I was able to borrow a computer from a friend of a friend, swapped proms and put it in my car. Sure enough two days (about two running hours with various startups/ shutdowns) of driving and no issues.
So I am now on the lookout for either a repair or reasonably priced replacement ECM.
Kind of sucks cause that seems to be the only problem with the ECM.
I just confirmed the ECM is causing the QDM Code 26.
My service engine light comes on consistently, every time I drive it. Sometimes a minute in sometimes a few minutes but I know it will come on every time.
I was able to borrow a computer from a friend of a friend, swapped proms and put it in my car. Sure enough two days (about two running hours with various startups/ shutdowns) of driving and no issues.
So I am now on the lookout for either a repair or reasonably priced replacement ECM.
Kind of sucks cause that seems to be the only problem with the ECM.
Glad you figured it out. Yeah the ECMs on 92-93s are unique and becoming harder to find. The ones on ebay are stupid prices. If you can find someone parting out a Corvette or find a Camaro or Firebird of the same years with the LT1 and you can use those ECMs as well.
SIA can evaluate and repair, but that's up to $400+ these days.
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1992 Quad Driver Module Diagnose with Tech 2
