1993 TrasSport 3.8L Quad Driver Codes 26 and 56

[tinkering]

1993 TransSport 3.800
Has somebody got the correct list of code definitions for this van?
I did a forum search to no avail. I did a google search to no avail.
My old girl has codes 17,18,26,and 56.
It starts right up and runs fine but a few miles down the road starts to limp.
I love this old thing. I am going to clean 'er up and go around with 'er again for awhile.

[Stealthee]

Code 12 No distributor reference pulse (diagnostic test active)
Code 13 Oxygen sensor circuit open or no activity
Code 14 Engine coolant temp sensor error (high temp indicated)
Code 15 Engine coolant temp sensor error (low temp indicated)
Code 16 System voltage too low
Code 17 Camshaft position sensor error
Code 21 Throttle position sensor error (signal high)
Code 22 Throttle position sensor error (signal low)
Code 23 Intake air temp sensor error (low temp indicated)
Code 24 Vehicle speed sensor error (open circuit or no activity)
Code 25 Intake air temp sensor error (high temp indicated)
Code 26 Quad Driver Module (QDM A) error
Code 28 Auto transmission range pressure switch error
Code 31 Wastegate solenoid circuit error
Code 31 Gear Position Switch (PRNDL) error
Code 32 Baro sensor circuit error / EGR circuit Error / MAP sensor signal open
Code 33 MAP sensor circuit error (signal high indicating low vacuum)
Code 34 MAP sensor circuit error (signal low indicating high vacuum)
Code 35 IAC problem or idle error
Code 36 MAF sensor error / 24x crankshaft position sensor circuit error / 4T60-E Shifting error
Code 37 TCC brake switch circuit error
Code 38 TCC brake switch circuit error
Code 39 Clutch switch circuit error / Torque converter clutch error
Code 41 Ignition control error / MEM-CAL error / C³I Cam Sensor Signal error
Code 42 Ignition bypass circuit error
Code 43 Knock sensor error
Code 44 Oxygen sensor error (lean condition indicated)
Code 45 Oxygen sensor error (rich condition indicated)
Code 46 Pass-Key II (VATS) system error - circuit out of freq range
Code 47 UART (serial data) circuit error
Code 51 PROM error / Incorrect MEM-CAL
Code 52 Fuel cal-pak incorrect or missing
Code 53 System voltage too high
Code 53 Digital EGR valve solenoid 1 error
Code 54 Fuel pump circuit low voltage / Digital EGR valve solenoid 2 error
Code 55 ECM error / Digital EGR valve solenoid 3 error
Code 56 Quad Driver Module (QDM B) error
Code 57 Boost control error
Code 58 Trans fluid temp sensor circuit error (low voltage) / VATS system error
Code 59 Trans fluid temp sensor circuit error (high voltage)
Code 61 A/C system performance
Code 63 Right bank O2 sensor circuit error / MAP sensor circuit signal voltage high (low vacuum indicated)
Code 64 Right bank O2 sensor lean exhaust indicated / MAP sensor circuit signal voltage low (high vacuum indicated)
Code 65 Right bank O2 sensor rich exhaust indicated
Code 66 A/C pressure sensor circuit error (low pressure indicated)
Code 67 A/C pressure sensor circuit error
Code 68 A/C clutch relay circuit error (shorted to ground)
Code 69 A/C clutch relay circuit error (open circuit indicated) / A/C high pressure switch error
Code 70 A/C pressure sensor circuit error (high pressure indicated)
Code 71 A/C evaporator temp sensor circuit error (low temp indicated)
Code 72 VSS signal circuit error
Code 73 A/C evaporator temp sensor circuit error (high temp indicated)
Code 75 Digital EGR solenoid #1 circuit error
Code 76 Digital EGR solenoid #2 circuit error
Code 77 Digital EGR solenoid #3 circuit error
Code 79 Transmission fluid over temp
Code 80 Transmission component slipping
Code 82 3x crankshaft position sensor circuit error
Code 85 PROM error
Code 86 ECM Analog/Digital error
Code 87 EEPROM error (flash memory error)
Code 90 TCC error
Code 93 Transmission pressure control solenoid circuit error
Code 96 Transmission system voltage low
Code 98 Invalid PCM program
Code 99 Invalid PCM program

[tinkering]

17 Camshaft Position Sensor error
Is the CSP Sensor easy to get at?
18 Where is code 18?
26 What is QuadDriver Module A?
56 What is QuadDriver Module B?

[tinkering]

I just found a code definition list for 93 Trans Sport 3.8L at
https://www.troublecodes.net/gm/
Scroll way down the page.

17 Ignition control system, reference signal -circuit malfunction Wiring, poor connections, ICM, ECM

18 Camshaft position (CMP) sensor – circuit malfunction Wiring, CMP sensor, mechanical fault, ECM

26 Engine control module (ECM), quad driver/ output driver -circuit malfunction Wiring, ECM controlled components, ECM

56 Engine control module (ECM), quad driver/ output driver -circuit malfunction Wiring, ECM controlled components, ECM

[Tech II]

Quad driver faults tend to lead towards an ECM......

Basically, a Quad driver commands up to 4 different circuits......if the quad driver gets the wrong data from a circuit, it sets a quad code.....

Not easy to diagnose....proper testing, is you isolate each circuit the quad driver runs.....you activate the circuit by grounding it with an ampmeter....you observe the current for up to 10 minutes, and if current goes out of range, you found a problem circuit.....

For example, suppose one of the circuits controlled is a relay...lets say the coil of the relay shorts out and now current is high.......the quad driver detects this, shuts down the circuit, and sets the code.....this is labor intensive, and most techs would just swap out an ECM from another vehicle(must be the same number, and if the PROM is different, have to swap them also), and if it took care of the problem, then they would just order an ECM, with the latest PROM for it.....

Like I said, more often than not, it's the ECM.......but with this time and mileage on it, it could be the circuit, a component in the circuit, or a bad connection also.....like I said, not easy to diagnose.....

[tinkering]

Tech II,
That is Great info.
Where is access to the ECM? Under/behind the glovebox?

[LMP]

THios is the actual code list from the '93 tranport shop manual
www.avigex.ca/xport/3800codes.jpg
and dtc troubleshoot
www.avigex.ca/xport/dtc17.jpg
www.avigex.ca/xport/dtc18.jpg
www.avigex.ca/xport/dtc26.jpg
www.avigex.ca/xport/dtc55.jpg
www.avigex.ca/xport/dtc56.jpg
dtc56 usually refers to a failed section of the exhaust recirculating valve. The quad driver is not the culprit; it is the circuit that it controls that has failed and the fault is sensed at the driver level.

[tinkering]

Originally Posted by LMP

THios is the actual code list from the '93 tranport shop manual
www.avigex.ca/xport/3800codes.jpg

... and where is the ECM located?

[LMP]

It is behind the glove box, high on the firewall.

But all quad driver fails almost NEVER (in my case absolutely never) mean a fault of the drivers, but a fault of the elements or circuit controlled by the drivers. I never had to go to the ECM itself, excpt to its intermediate plug C111

www.avigex.ca/xport/c111.jpg
www.avigex.ca/xport/c111b.jpg
on the engine side (firewall, above passenger wheel bowl) to take measurements by removing the plastic cover. C110 (same model) is also used as intermediate, near the passenger side headlight..but I never went to that one.
THe EGRvalve is the classic problem with DTC56, and purge canister valve with DTC26.
Some of DTC56 are related to transmisison control...but if all shifts are OK, then problem not transmission side.
To test EGR valve, pull plug from valve, D (from DTC55 page) is ground, A,B,C are the coils. I remember two coils are 25 ohms and one 12 ohms. It happens one of them is broken..infinite ohms. In one occasion the fail was with the plug contacts.

[Tech II]

LMP, I have to disagree....those late 80's and early 90's PCM's were notorious for failures.....If you were lucky, a "tap test" would verify it....

But seeing how this PCM is 25 years old, chances are in it's lifetime it has been replaced....in fact, I would not be surprise if the label on it states "Reman".....

And as I stated before, I agree with you, every circuit would have to be checked out on the quad drivers to diagnose which could be labor intensive.....could be something as simple as a connection....but finding it is like a needle in the haystack....

And you would need wiring diagrams, a good meter, and the expertise to do the tests......only thing that saves your butt is a visual inspection, that shows something obvious....

[tinkering]

Originally Posted by LMP

THios is the actual code list from the '93 tranport shop manual
www.avigex.ca/xport/3800codes.jpg
and dtc troubleshoot
www.avigex.ca/xport/dtc17.jpg
www.avigex.ca/xport/dtc18.jpg
www.avigex.ca/xport/dtc26.jpg
www.avigex.ca/xport/dtc55.jpg
www.avigex.ca/xport/dtc56.jpg
dtc56 usually refers to a failed section of the exhaust recirculating valve. The quad driver is not the culprit; it is the circuit that it controls that has failed and the fault is sensed at the driver level.

Thanks LMP
That is invaluable information.
I need to take a look at that old EGR.

[tinkering]

Originally Posted by LMP

It is behind the glove box, high on the firewall.

But all quad driver fails almost NEVER (in my case absolutely never) mean a fault of the drivers, but a fault of the elements or circuit controlled by the drivers. I never had to go to the ECM itself, excpt to its intermediate plug C111

www.avigex.ca/xport/c111.jpg
www.avigex.ca/xport/c111b.jpg
on the engine side (firewall, above passenger wheel bowl) to take measurements by removing the plastic cover. C110 (same model) is also used as intermediate, near the passenger side headlight..but I never went to that one.
THe EGRvalve is the classic problem with DTC56, and purge canister valve with DTC26.
Some of DTC56 are related to transmisison control...but if all shifts are OK, then problem not transmission side.
To test EGR valve, pull plug from valve, D (from DTC55 page) is ground, A,B,C are the coils. I remember two coils are 25 ohms and one 12 ohms. It happens one of them is broken..infinite ohms. In one occasion the fail was with the plug contacts.

I will run the ohm tests on the EGR, and on the connector as you say.

I will see if there is a good looking EGR valve at the 'pick yerself' wreckers, and a Purge Canister valve too.



Is the purge canister valve right at the canister or...? How do you test it?

I remember the gas tank isn't venting properly; it builds up a vacuum which is very apparent when you open the gas cap when low on fuel. Is that related to the purge can valve code 26?

Thanks for the picture and diagrams of the black plastic PCM intermediate connector on the wheel well? Do you use that to test the QDrivers?

[tinkering]

Originally Posted by Tech II

LMP, I have to disagree....those late 80's and early 90's PCM's were notorious for failures.....If you were lucky, a "tap test" would verify it....

But seeing how this PCM is 25 years old, chances are in it's lifetime it has been replaced....in fact, I would not be surprise if the label on it states "Reman".....

And as I stated before, I agree with you, every circuit would have to be checked out on the quad drivers to diagnose which could be labor intensive.....could be something as simple as a connection....but finding it is like a needle in the haystack....

And you would need wiring diagrams, a good meter, and the expertise to do the tests......only thing that saves your butt is a visual inspection, that shows something obvious....

I am going to leave the actual PCM til last because of the cost of the thing but I will see if there is a unit at the pick yerself that I can use to swap test the codes. I had to change one out on a similar year Buick once.


I'll do a bit of connection testing in the haystack but hopefully I don't have to get into any of the QDriver testing proceedures. It sounds like a big job. Thanks for that!

[tinkering]

What are the most common component problems associated with codes 17 and 18?

[tinkering]

Originally Posted by LMP

THe EGRvalve is the classic problem with DTC56, and purge canister valve with DTC26.
Some of DTC56 are related to transmisison control...but if all shifts are OK, then problem not transmission side.
To test EGR valve, pull plug from valve, D (from DTC55 page) is ground, A,B,C are the coils. I remember two coils are 25 ohms and one 12 ohms. It happens one of them is broken..infinite ohms. In one occasion the fail was with the plug contacts.

The closest resistance readings of the 3 coils that I could find was 50 ohms on two and 25ohms on one. Does that sounds feasible? I remember changing the EGR valve and solenoid cluster 5 or 6 years ago.

There is an ugly transmission shift that happened a few times times on the highway (I think I started a thread on it way back when). When using the passing gear in the mountains it would pound back into cruise quite vehemently! I am going to change the vacuum modulator valve on the side of the transmission to see if that eliminates that occurrence.

Is there a transmission control module, a TCM or something similar?