Check Engine Light - What Next

[jeffs2002]

I have replaced, all 3 coil packs, ICM, camshaft position sensor, crankshaft position sensor, throttle position sensor, O2 sensor, PCV valve, IAC, MAF, EGR, plugs & wires and PCM and still after driving about 2 blocks my check engine light still comes on. No one can figure this out. Any other ideas?

[Mickey#1]

What year/model?
What's the code?

[jeffs2002]

1994 Park Avenue Ultra. I had it scaned again and it came up showing a bad quad driver #1. This is a brand new PCM (3rd one).

[Mickey#1]

Quad driver's are mini-relays built into the PCM. Each driver controls up to four devices. If you've replaced the PCM for that same code then the problem is probably one of the four devices & not the quad driver itself. You need to know which four devices are connected to that quad driver then you can check the resistance of those devices & see which one is out of whack. Some posibilities are transmission solenoids, fuel pump relay, egr solenoid, fan relays and maybe the fuel injectors.

Edit - I did a little searching & these may be the devices connected to QDM1:
Torque convertor clutch
Evap purge solenoid
Boost control solenoid - I'd check this one first, resistance should be around .5 to 1 ohm.

[Thom54]

When you changed out the PCM did you swap the PROM from your old one to the new one, Had the same problem on a 94 when I forgot to change the PROM lucky for me I had not throw my old PCM away.