I took my '93 Z to a local automotive shop the other day because my service engine light comes on every time i start the car, but it wont output any codes when i try the onboard diagnostics. The only code it gives back is code 12, which is supposed to mean the diagnostics is working. Anyway, the shop told me that their tests resulted in a "code 26" and that the #1 Quad Driver was bad.

Can someone tell me if this makes sense? They said the quad driver that contols egr system and fans was the one that was bad. My fans do come on and function however.

Also, what does thier "code 26" mean?

Is all of this something that can be resolved with a custom chip from pcm4less for example?

 

The shop is right AND wrong. A 26 is a quad driver fault but #1 is not the driver for the fans. It is the one for the Air pump, EGR solenoid and EVAP solenoid. The number #3 quad driver is the one for the fans and the AC. But that would be DTC 28.

Also a quad driver fault does NOT always mean the ECM is at fault. Remember the ECM has a sense line at the output to detect if the voltage is at the inticipated level. If it is not, it sets the fault. I'll put money on switching ECM's won't solve the problem.

I think there is a fault in one of the circuits the driver is connected to.

What you're gona need is a schematic for the circuits in question and start poking around with a multimeter.

I don't understand why you got a "12" which I believe doesn't exist but didn't get the "26". Could it be you didn't catch the blinking pattern correctly?

 

The haynes manual states that Code 12 means the diagnostics is working properly. It is not a true trouble code. It is supposed to flash code 12, 3 times then start flashing true trouble codes at you. All i ever got was a repeated 12, which the manul says means no problems.

If a quad driver is bad, does that mean that those systems will not function? In my case, does that mean that the egr, air, and evap are not working?

 

As was already pointed out... could be a faulty Quad Driver module, or it could be a fault in the electrical circuits to any one of those three devices. Given the fact that a blown AIR pump fuse it the most common cause of an SES light, I'd start by looking there.

 

I understand that the SES code could represent either of the two situations. My question is if the quad driver is truly bad, does that cause those systems to be inoperable?

Also, Speedy suggests "poking around with a multimeter." What kinds of things should i be looking for and testing?

 

Can't say it much clearer. You need a schematic to figure out which wires going to the ECM to probe. You check them for the correct voltage.

As far as the systems effected by the fault. If the quad driver was bad it could be bad in 2 possible ways. The output circuit could be a problem, in which case the device is not turned on. Or the sense line could be a problem, in which case the device comes on as requested by the ECM but the ECM can't detect that the device did so.

As was pointed out, you should start with the air pump. It seems of the 3, it is more likely to crap out.