What is code 26
I'm sure the website cited will be of help. The infamous code 26 quad driver comes up pretty frequently on the Saturn Mailing List. One of the better technical explanations for pre-OBDII Saturns has been quoted several times. Here is the message, edited somewhat:
(credits to Ray Prill)
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> Yesterday, I saw my first Service Engine Soon light.
> I checked what code my car had stored, and it was #26.
> Code 26 (according to Haynes):
> Quad Driver output fault
> Possible cause: The PCM detects an improper voltage level on the circuit that
> is connected to the Quad Driver Module.
> Now, my questions are... What IS the Quad Driver Module, what does it do, and
> where is it?
Pretty vague, isn't it?
First of all, don't panic. Usually, this is not a serious
problem. Let me explain.
Code 26 is a *very common* SES indication to get with a Saturn that
has a few years on it. Most of the solutions, luckily, are not costly.
However, this may depend on the year of your car.
The "Quad Driver" is a device in the computer that "drives" electro-
mechanical devices in the car. Computers run with very little current
(milliamps or microamps) in their circuits. But the devices that
turn on your cooling fan, bulbs, or emissions relays may require
current in a higher range, say tenths of an amp.
Thus, the computer can't talk very well with such a high current
device. It needs help, and it gets in in the form of this Quad Driver
device. The computer sends a signal (very low amps) to the driver, and
it in turn then signals the electromechanical device to do whatever it
needs to do with a higher current which that device can use.
It sort of "drives" the device by remote control.
OK, fine, that is the theory. So why the code 26? Well, in almost all
cases, the actual driver device does not fail. What fails is one of
the electro-mechanical devices attached to it. The way the SES light
works, it will come on when either one of the driven devices fails or
if the driver itself fails.
The good news is it is usually not the costly driver device. The bad
news is this is called a "QUAD" driver. That means it drives four
devices. Even worse, there are usually TWO quad drivers, so you have
a total of EIGHT devices to check for just this one SES light.
That's right, code 26 means that one of 8 devices (and a 9th, the driver
itself), could cause the problem. You have to check 8 different things.
I don't have my manual here, but I'll try to remember to post the
exact devices to check. The following is from memory, so bear with me.
Also, remember my car is a '91, so this may have changed somewhat in
The QD generally drives things like relays, solenoids and light bulbs.
There are a few things that are easy to check, like the bulbs and
The SES bulb and (I think) "HOT" bulb are driven by this device. You
should check that they both come on when you put the car to "on" before
starting. Of course, the SES must work, since it came on for you.
Then the A/C relay and Cooling fan relay are driven. For A/C, simply
check that your A/C works OK. The relay is pretty silent, unlike
some cars, so you can't always hear it click. Just make sure it works.
The cooling fan can be checked when you sucked out the code. Since you
know how to get the code, you should have noticed that the FAN comes
on for a while before getting the code out. (The bulbs also light.)
If the fan isn't coming on, check the relay. The Haynes manual probably
tells you exactly when the fan comes on during the procedure.
The relay is accessible in the under-hood fuse block.
After that, it gets tougher. You have to check some emissions solenoids.
From what I've read, the MOST COMMON cause of code 26 is either the
EGR solenoid or the canister purge solenoid. The EGR solenoid is
real easy to access. It sits right above the EGR valve and takes a minute
to disconnect on Sx2 models. The canister purge solenoid is a pain.
It is attached to the block on the firewall side. You have to take it
out blindly by putting your hand through a small "hole" between all the
hoses and wires.
I forgot what else is controlled by this device. I'll try to get
my manual tonight to look.
I had an SES light last spring. In my case, I guessed wrong.
I narrowed my SES last year down to the CPS or the EGRS, and incorrectly
deduced the CPS. What a pain to replace this. But I was wrong. That
wasted $20. My problem was the EGRS, and it was also a $20 part. Very
easy to replace.
I should mention that my symptoms were opposite of yours. Mine would
come on only while driving for a while, then go off when I stopped.
I should also mention that the CPS and EGRS are common causes of
code 26, and the irony is they are both Nippondenso parts, made in
Japan. How ironic!
Either way, if you take it for service, the Saturn diagnostic computer
should be able to discern between the two or any other device that
is causing this code. They can read more information than we can
by just pulsing out codes.
So, depending on your skill and your luck, you may or may not want to
try this. Like I said, most of the them are easy, thus even if Saturn
service does it, it usually is not costly.
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And a followup:
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This is a follow up to yesterday's post about a "quad driver" fault.
Yesterday I mentioned the causes for a "code 26" fault with the
SES light. There I detailed the following causes:
1) SES light burned out
2) "HOT" light burned out
3) A/C relay
4) Coolant fan relay
5) EGR solenoid
6) Canister purge solenoid
I couldn't remember the other two causes. Remember, the "quad" in
the driver means it controls 4 outputs. Since there are 2 QDMs,
they control 8 outputs.
The other missing items to check are:
7) Speedometer output
8) Upshift/Shift to D2 bulb
Hope this helps. As you can see, most items are easy to
check except for the solenoids. These can be checked by
measuring their resistance.
Apr 21, 2009 |
1995 Saturn Sl