93 Vette pulled a code 26 QDM fault

[tim1]

I took my vette to a parts store and asked to have a diagnostic test run. They found a 26 QDm fault. The guy looked in their book and it shows as a Quad Driver Circuit, and states dealer service required. So my questions. What is the quad driver circuit, what does it do and is the dealer the only ones that can correct whatever the problem might be???? I have only had this car for a couple days and want it to be correct going down the street.
Thanks for all the help.

 

[vetteoz]

What is the quad driver circuit, what does it do

From another site
GM vehicles.
Quad driver fault; is the computer really the cure?

Probably not but, if the vehicle is early gm and has a constant check engine light with a quad driver fault code set the computer (ECM) may have became permanently damaged.
So if the ECM is replaced without any diagnosis to locate and repair the cause of the fault then the new ECM may soon become permanently damaged as well.
On newer vehicles with an ECM that has protected quad drivers replacing the ECM is most often not necessary.

There are many different code charts out with different code definitions. Some are quite vague while others seem over complicated. Some simply state, quad driver fault, while others will state, quad driver circuit fault, sense voltage low when should show high. Or sense voltage high when should show low.

No mater how the description reads when a quad driver fault is set, then quad driver circuit testing is imperative before an ECM is replaced.

First let’s look at the ECM and its quad drivers. Most ECM controlled devices are either solenoids or relays.
Typically, solenoids are used for a circuit when the current draw is 0.75 amps or less, and relays are used in a circuit when the normal current draw is expected to exceed 0.75 amps. GM uses quad driver circuits inside the ECM to control the outputs to these devices.
So quad drivers (QD) are integrated circuits inside the ECM that it uses to close or open the circuit path to ground, turning the device on or off. Depending on the make and model year GM vehicles use different variations of quad drivers.
Quad drivers (QDR)
Are permanently damaged if a device or its circuit shorts, no added circuit protection.
Quad drivers II
Temporarily shut down and then reset if a device or its circuit shorts.
Quad driver modules (QDM)
Temporarily shut down, sets a fault code, and then resets if a device or its circuit shorts.

Lets look at testing quad driver devices and their circuits.

As we’ve all ready seen, most quad driver circuit faults are due to a short in a device or its circuit. (Wiring/connectors). However at times a device or circuit that is open will set a quad driver fault code.

Before replacing an ECM, always isolate the problem device or circuit. Replace the defective device or repair the circuit, and retest.

Each quad driver can control up to four devices. So diagrams will have to be used to find which devices the quad driver at fault is controlling.



A real diagram would list all circuit numbers, the wire colors, and connector terminal numbers. The important thing is that each device and circuit is tested, found to be good or repaired as necessary.
The proper test on these circuits would be, with key off disconnect all ECM connectors, then with an amp meter set on the 10 amp scale connected to the control side of the circuit at the ECM connector and to ground turn the key on and check that the device turns on.
With the device turned on, the meter should read 0.75 amps or less. Run this test for at least five minutes to make sure the device isn’t overheating and shorting.
The TCC solenoid cannot be tested in this manner in a vehicle that has a normally open third gear switch inside the transmission. A scanner thru an extended road test best checks the TCC circuit.

A normally operating device and its circuit will have at least 20 ohms of resistance and can be checked with an ohmmeter.
This will tell if the circuit or device is open however, this will not place the device in operation.
So if the device is only failing due to heat after being in use for a period of time the fault will not be found with a resistance test.

With the proper test equipment it’s fairly easy to determine what circuit or device is causing a quad driver fault.

You will need a good digital multimeter and, if this first time buy the best would be one that has a 20 amp fused capability. The larger amp rating can come in handy when testing other electrical systems of your vehicle.
Also two 10 amp fused jumper wires keeping the in-line fuse as close to the power supply circuit as possible.

The most important thing to have on hand is information! The best would be the factory service manual but these are expensive.

Just because you have a Quad driver code doesn’t mean the Quad driver is bad.
All a Quad driver code means is that an expected value is not present when it’s suppose to be.
Also a Quad driver is a techy name for 4 on-off switches arranged in a group, hence the name Quad driver. The computer watches the voltage values on each switch and knows that if the switch is on, a voltage value will be seen.
When the switch is off the opposite voltage value will be seen.
Simply put, light on, light off.
So what can set a quad driver code? You’d be surprised. How about a bad bulb?
How about a bad fuse? The answer is yes to both questions.
Yes, a bad bulb or failed fuse can set a Quad driver code.
Start with checking your fuses.
There can be up to 3 fuses that supply power to circuits controlled by the Quad drivers.
If the fuses are good the next check would be of all or some of the following, depending on how your vehicle is equipped:
Up shift light bulb, coolant hot bulb, shift to drive bulb, A/C relay, coolant fan relay, EGR solenoid, Canister Purge solenoid, even a speedometer output signal goes to one of the switches on the Quad driver.
It’s more likely that the Quad driver code is present because the computer is not seeing the information that it expects to see at one of the switches.

Quad/Output Driver Module:
The Control Module in this vehicle controls most components with electronic switches which complete a ground circuit when turned on.

When the switches are arranged in groups of 4, they can independently control up to 4 outputs and are called Quad Drivers.

When the switches are arranged in groups of 7, they can independently control up to 7 outputs and are called Output Drivers.

Not all outputs are always used.

 

[tim1]

Looks like I am taking it to the dealer to let them do it. Sounds like alot of unknowtesting for me to do. Thanks for the information.

 

[gmjunkie]

Looks like I am taking it to the dealer to let them do it. Sounds like allot of unknowtesting for me to do. Thanks for the information.

grounds,Grounds,GROUNDS,If you have a Non-existent or High resistance Ground,It'll make electronic controlled things do weird SH*T!~!!
Inspect and CLEAN All GROUNDS!
ALL of THEM,Even the ones you can't see!~!!



While your at it clean and inspect All wiring connection plugs and fuse connections too!~!!

 

[tim1]

I can check alot of the grounds that I can find. The bigger part of the problem is I just became a Vette owner on this past Friday and have no under the hood time at all. I guess I will pull it out of the garage and start looking for anything that appears to be a ground wire or connection and hope for the best. I think an owners manual and tech book would be of great help for wiring diagrams. Anybody got a wiring diagram for a 93 Vette? Sure might help me out.

 

[gmjunkie]

You will need to remove the battery and some trim pieces to get them all!~!!
(Ground Connections are the ones with a G first!)
I just stoled this from 1 of John Robinson's posts,It should help!~!!

Thanks John!~!!

 

[Hib Halverson]

Welcome to the CAC "tim1".

One clue which was not in your OP was whether or not the MIL (check engine light) was on when you went to the parts store for a scan.

Was it?

If it wasn't, the DTC26 might be a history code. In that event, I'd clear codes, road test and continue to monitor the issue.

If the light was on and if you purchased the car from a dealer, I'd take it back and demand they repair the vehicle. If you bought it "as-is", and you have some DIY engine diagnostic experience, first, I'd buy a copy of the 1993 factory service manual (Zip Products sells them) then I'd take the advice given by others here and look for a bad ground. If you don't find a problem there, use the diagnostic info in FSM Section 6E to troubleshoot code 26.

Good luck!

 

[tim1]

THanks John and GM Junkie! Now I can print out this thread and get some checking done. When I took it to the parts store the (might be wrong)ASR light was on and nothing else. The PO said his mechanic checked everything and nothing was wrong. Sounded funny to me a light is on and nothings wrong. Thats why it went to the part store for testing. Now I have a bit of testing and checking to do.
Thanks for all the help hopefully I can find the culprit and correct it now.

 

[boomdriver]

Go straight to the G104 grounds...you may have to hunt a bit. This stack is on a bolt near the oil filter..its on the block or trans housing somewhere near the oil filter. It has 3-5 ground wires, including the ECM, dash, injection, and other critical grounds.

I'd also check the jump-post behind the battery for loose 'hot' wires.

 

[gmjunkie]

Go straight to the G104 grounds...you may have to hunt a bit. This stack is on a bolt near the oil filter..its on the block or trans housing somewhere near the oil filter. It has 3-5 ground wires, including the ECM, dash, injection, and other critical grounds.

Broom,We'll have to agree to disagree here!~!!He needs to Clean and Inspect ALL the Grounds here,This is the southeast!~!! Home of 3 million % humidity and salt spray blowing in off the Atlantic!!!

When I took it to the parts store the (might be wrong)ASR light was on and nothing else. The PO said his mechanic checked everything and nothing was wrong. Sounded funny to me a light is on and nothings wrong. Thats why it went to the part store for testing. Now I have a bit of testing and checking to do.

Dose it have the right size tires on it all the way around?~?? Wrong size tire on the front or rear will sure screw with the ASR's head!~!!:L:L:L

 

[tim1]

Well I have yet to be able to get anything done with the grounds as of yet. I have done a bunch of researhing and asking of questions. Things I do know about this car. The brakes are very hard to push, not like regular power brakes. The tires are not the stock size nor are the same front and rear. I was told that there should be 2 pieces of paper stuck inside the center consule that would allow me to have everything identified about the Vette, no papers in the center consule and non in the glovebox. I found a master Gm mechanic that wants to diagnose the ASR service light next wekk to ry to determine what is actually wrong with it. I really do not want to have to pay to get it corrected but that looks like the next course of action. Sure wish I could get it right without having to go through a shop.

 

[Hib Halverson]

THanks John and GM Junkie! Now I can print out this thread and get some checking done. When I took it to the parts store the (might be wrong)ASR light was on and nothing else. The PO said his mechanic checked everything and nothing was wrong. Sounded funny to me a light is on and nothings wrong. Thats why it went to the part store for testing. Now I have a bit of testing and checking to do.
Thanks for all the help hopefully I can find the culprit and correct it now.

Parts stores typically used cheap scan testers which do not support ABS/ASR. It is likely that if the Service ASR light is on and the mechanic said nothing was wrong, he/whe was using a tester which doesn't support ABS/ASR.

In any event, you may need a tester which supports ABS/ASR and the factory service manual if you are going to attempt a DIY repair.

 

[gmjunkie]

Well I have yet to be able to get anything done with the grounds as of yet. I have done a bunch of researhing and asking of questions. Things I do know about this car. The brakes are very hard to push, not like regular power brakes. The tires are not the stock size nor are the same front and rear. I was told that there should be 2 pieces of paper stuck inside the center consule that would allow me to have everything identified about the Vette, no papers in the center consule and non in the glovebox. I found a master Gm mechanic that wants to diagnose the ASR service light next wekk to ry to determine what is actually wrong with it. I really do not want to have to pay to get it corrected but that looks like the next course of action. Sure wish I could get it right without having to go through a shop.

Have you looked in the compartment behind the passenger seat,sometimes the RPO tag is there!! You can find out the original tire size from the tag on the rear of the drivers door!! What size tires are on it now??
I'm heading to FLa real soon,Where you at in GA,I'll be rolling through GA with my diagnostic computer!

I'll PM you my cell, Call Me!~!!