My 1991 Pontiac Bonneville gives me a Code #26 (Quad-Driver-Module-1) and a Code #39 (Torque Converter Clutch).

My transmission shifts really soft 1-2; 2-3; 3-4 all the gears as it should be. At more or less 60 to 65 mph it should lock into overdrive, but it won't. If 70+ mph are reached, I've to give it a hard kick to the gas pedal, sometimes the overdrive (TCC) locks in and the rpms go down. If I lower my speed below 60 mph the overdrive (TCC) locks out like normal, but don't locks in again, if I increase the speed, so I have to start the 'kick-down-sequence' again to lock in the overdrive (TCC). There is no SES light on.


Another symptom: with key in position 1 all the required safety lights come on, like battery, coolant temp, SES, door open... Whem I turn off the engine after an e.g. 10 miles ride, and turn the key to position 1, the SES light doesn't come on, but all the other safety lights are working. If you let the car sit for a while, the SES light is back on in key position 1.


Is anybody able to guide me, how to find out, if the issue is related to a faulty EGR, Torque Converter Clutch, TCC Solenoid or ECU.

Any test procedures are welcome.

Many thanks.

Code 26: QDM A error
Code 39: TCC error

I'd bet the two are related, but first:

- How old is the battery?
- How many volts are read at idle in Park with headlights on and blower on high?

Voltage issues can affect the QDM.

You like have a bad TCC solenoid. Do you have a dvom?

The battery 75Ah is two years old. It holds 12.5 - 12.7 volts over night. With engine runing I get 14.2 volts from the alternator, which seems to be fine so far.
Yes, I've a digital volt meter. I think the 5-pin plug in front of the transmission (it'* a 4t60e) is the connection between ECU and the solenoids inside the transmission.
Fyi: the transmission was rebuild less than two years ago. I put it out by myself (it was a terrible work) and toke it to a transmission shop. It was necessary, because the PRND-switch jumped out of it'* position and couldn't be moved to any position. At this time the odometer was reading 150k miles (160k miles, now). When the shop opened the tranny they told me, there is no wear on anything inside the transmission and they just need to put the PRND-switch back into position. I asked them to put new solenoids, clutches, bands, chain, etc. in, because the transmission is open and they have easy access to everything inside. When I picked it up, they just put new clutches in and told me again, there were no need to replace any other stuff... - They're all idiots, toke $2,000.- out of my pocket for nothing (sorry for that, I'm just frustrated).
However, do you know, which pin at the plug will give me access to which of the solenoid? - Like to check them all.
If I will get a negativ output from the check and solenoids have to be replaced. Is it possible to drop the side pan with the transmission in the car?
What would you say, should all solenoids be replaced, or just the faulty one? - I know, hard to say, if your not able to read the future out of a glas-bowl
Thanks for your replies.

Here'* the diagrams. Myself I would replace it all. You can do this in the vehicle. You have to remove the axle and the strut and possibly a mount or two to loser it down on that side,

Many thanks for the diagrams. I'm a bit irritated, because the Quad-Driver-#1 (code #26) is just monitoring the canister purge valve, the SES light and the fan relais. - I put on new fan relais, a new canister purge valve and a new SES bulb, but code #26 still comes up (all new parts are really new out of the box). - I have them in my private stock). Got the old parts tested and they also work fine...? I checked the wiring and 12 volts and ground connection is also given.

Regarding the TCC-solenoid (code #39): until now, I can say the 15 amp fuse is okay, because the brake switch works during my road test. - I had my right foot on the acceleratior and slightly touched the brake pedal with my left foot, just to that point when the brake lights come ON and the rpms jumped up around additional 400 rpms.

By the way... I'm located in Germany. The easiest way to buy parts for my car is to order them online. My prefered parts dealer is RockAuto, because they ship really fast and they have a good support.
I found a solenoid set from PIONEER (#771041) including four solenoids and they show me a single solenoid AC DELCO (#2141464) which is not included in the PIONEER-set. Does it mean, I need five solenoids in sum?
In some comments along different forums, some people where talking about SONNAX solenoids are the best, especially regarding the TCC solenoid. - Do you have any information regarding this?

Many thanks

You'll get a code 26 if any of the quad driver circuits are not functioning correctly. Did you check the resistance of the TCC solenoid?
As for brands I like delco as that would be OEM.

Here'* the wiring diagram. Shows lower right the AT. Switches and the TCC is all there is.

The PIONEER is a full set of solenoids, the DELCO is a single solenoid, but looks different to all that solenoids from the PIONEER-set. Does it mean I've to order both?

I don't checked the solenoid until now. Do know which pin at the plug on the transmission need to be checked?

Sorry, didn't saw the wiring diagram you sent. Seems to be the Tan/Black wire. I will check this tomorrow, it'* close to midnight here
Thanks a lot.