Cruise, A/C, ABS Electrical Problems

[LPelton]

93 Jeep Cherokee 4.0. All at the same time I lost my A/C system, my aux fan stopped, Cruise Control quit and the ABS light started shining on the dash. MIL codes are 33, 35, 36. When I turn on the A/C switch the engine speeds up like it is anticipating the clutch activation but nothing else happens. The clutch does not engage and the aux fan does not come on. I can jump the A/C relay and the clutch will engage (and cools) and the aux fan comes on. Fuses are all fine.
I have not done any troubleshooting on the cruise control yet. The ABS pump does not seem to be activating. I dont feel it vibrating anymore. I can reset the PCM and the ABS light comes on immediately. I am guessing there is one sensor common to all of these systems causing the problem. I checked the TPS and it seems to be fine. Not sure what else to check. I heard the wide open throttle relay might be bad but I dont think this vehicle really has one. I am beginning to think the computer may have gone bad. Any suggestions?

	Throttle position sensor A throttle position sensor (TPS) is a sensor used to monitor the position of the throttle in an internal combustion engine. The sensor is usually located on the butterfly spindle so that it can directly monitor the position of the butterfly throttle valve. The sensor is usually a potentiometer and therefore provides a variable resistance dependent upon the position of the butterfly valve (and hence throttle position). The sensor signal is used by the Engine Control Unit (ECU) as an input to its control system. The ignition timing and fuel injection timing (and potentially other parameters) are altered depending upon the position of the throttle, and also depending on the rate of change of that position. For example, in fuel injected engines, in order to avoid stalling, extra fuel may be injected if the throttle is opened rapidly (mimicking the accelerator pump of carburetor systems).

[Bounty__Hunter]

33* An open or shorted condition detected in the A/C clutch relay circuit.

35* An open or shorted condition detected in the radiator fan relay circuit.

I had a tough time finding anything on #36, only thing I found close to being related to your symptoms is:
36* A/C Request Signal Voltage Low

Have you replaced any of the relays to see if that fixed the problem? The AC and ABS relays are there together, and maybe the Cruise, so something could have damaged all of them at the same time.

I've got the cruise control solenoid from a '93 XJ I parted out, if you need it. A lot of other '93 XJ parts if you need anything else.

[LPelton]

[quote="Bounty__Hunter"]33* An open or shorted condition detected in the A/C clutch relay circuit.

35* An open or shorted condition detected in the radiator fan relay circuit.

I had a tough time finding anything on #36, only thing I found close to being related to your symptoms is:
36* A/C Request Signal Voltage Low

Have you replaced any of the relays to see if that fixed the problem? The AC and ABS relays are there together, and maybe the Cruise, so something could have damaged all of them at the same time.

IThanks, all the relays are good (I have not checked the ABS relay but it has power where it is supposed to). I did not try to take teh relay box apart to see if something was wrong inside. The incoming signal to the relays is what appears to be missing. The cruise control is only about 2 years old. That is why I am trying to figure out if it is a problem common to all three. Wide open throttle cutout for the A/C could be one but from what I can tell that is actually done by the computer. A brake switch seems to be common to the cruise and ABS system but not sure how the A/C ties in. Could be a problem in the wiring from the computer to the under hood relay/fuse box. When it stops raining long enough I am going to jump a wire from the computer output connector to the relay and see if it works. With such a wild range of problems (and it is very hard to get the MIL to flash consistent codes) I still have the bad feeling it is the computer. It was replaced a few years ago. Any ideas?

[Bounty__Hunter]

Sounds like it's upline from the relays then. Try to email or PM XJ_Nick on here, he's a go-to kinda jeeper for electrical issues.

[Saurian]

Is there one of those stupid maxi-fuses that might control those systems? Just a thought...

[LPelton]

Originally Posted by Saurian

Is there one of those stupid maxi-fuses that might control those systems? Just a thought...

Thanks, I checked all the large fuses. All appear good. I may change them out anyway. Should have done a continuity test on them. I will send XJ Nick an email and see what he thinks. I will be away from the Jeep for a few weeks so I may have to try again after the 14th of Feb.

[LPelton]

Thanks for everyones help. The solution was so simple I am almost afraid to post it. My mistake was that I only checked the fuses that were obviously part of the systems that weren't operating. For the heck of it I went down the entire under hood power center and checked every fuse. There is a small one marked "Ignition" It had blown. The second I replaced it everything was up and running. It always pays to check everything simple.