Hello all,

I am a brand new member although I have been reading in this forum for a few weeks trying to figure out this issue I am having with my Jeep. This forum has been very helpful in getting me where I am now but I am stuck and need help. Ill start with the back-story:

A good friend was using this jeep as a winter warrior. One night he backed into a tree coming out of an icy driveway. It ran as normal all next day and he drove it to work second shift. He went to go pick up a drink on a break and it died pulling out of the parking lot and would not start back up again. He didn't want to deal with it so he started searching for another vehicle and sold the jeep to me and another friend.

Now the details:

173k miles on a 4.0l inline six 4wd

Key on and the fuel pump kicks on and primes. There is pressure at the rail.

When cranking there is no spark (tested a plug while cranking) and I cannot hear the fuel pump running while we crank.

We have swapped the ASD relay with other working relays of the same part number and don't believe this is the issue as the fuel pump is kicking on.

All fuses are good in the engine bay (havent checked the panel inside the vehicle thouroughly

We tested the crank position sensor and it tested good. Cam sensor is reading changes in voltage when cranking but our digital gauge does not respond fast enough to tell us exactly what it is doing. we want to test this with an analog voltmeter soon. the fact that the voltage is changing on the cam sensor tels me it is sending a signal.

The coil tests good

The jeep is throwing 3 codes
P0122- TPS
P0505 - Idle air control
P0700 - Transmission management

We have readjusted the NSS as it wasn't always cranking in neutral and this symptom is gone now.

We replaced the TPS

All codes come back after clearing

I did something stupid today and threw a new crank position sensor on it today even though we were only experiencing 1 or 2 of the issues. I was running out of things to test and it seemed like every thread on similar issues that ended up resolved was a cps issue. Replaced it and no dice.

I think my next steps are to test the cam position sensor with an analog meter then its looking for wires to test continuity and the next culprit is the computer. The computer looks to be in good condition and all the connections and mounting hardware look good. I read people having issues with mounting bolts grounding it out but it doesnt look like that is happening, I guess I a m not sure what these bolts are supposed to be grounding to if that is the issue.

I wonder if any of you have a goo wiring troubleshooting guide or a way to test the computer to see if it is bad?

Any other ideas of things to check or whether any of these codes would cause a no spark?


I apologize for the dissertation, thank you for reading if you got this far.

 

P0700 is sort of a product of other codes being set and it may go away once the primary causes are eliminated, but look at the possible causes for P0122. I've highlighted one cause that may be related to P0700.

Here's some data on the other codes. I think you ment P0505, not 550.

P0505 looks like it's a PCM problem, or simply the IAC motor.

Of course you can't rule out chafed wires. Wiggling wire harnesses is a standard procedure for diagnosing trouble codes. Clear codes and wiggle wire harnesses (especially around the Throttle Body) and see if the codes stay away, or immediately return. Visually examine the wires in the engine bay for chafing.

P0122 may be a loss of the 5 volt supply to the TPS. You can check for voltage at the TPS connector. The body harness TPS connector pinout is shown below. With the connector detached from the TPS, and the ignition key to RUN (engine off), read from pin socket 3 to 1, or from 3 to engine ground. You should read approximately 5 VDC. The 'ground' listed for pin socket 1, Sensor Ground, is inside the PCM.



P0505-IDLE AIR CONTROL MOTOR CIRCUITS

Possible Causes

IAC MOTOR WIRING HARNESS OBSERVABLE
IAC MOTOR WIRING HARNESS INTERMITTENT
IAC #1 DRIVER CIRCUIT SHORTED TO #2, #3, OR #4
IAC #2 DRIVER CIRCUIT SHORTED TO #3 OR #4
IAC #3 DRIVER CIRCUIT SHORTED TO #4
IAC MOTOR
IAC #1 DRIVER CIRCUIT SHORTED TO GROUND
IAC #2 DRIVER CIRCUIT SHORTED TO GROUND
IAC #3 DRIVER CIRCUIT SHORTED TO GROUND
IAC #4 DRIVER CIRCUIT SHORTED TO GROUND
IAC #1 DRIVER CIRCUIT OPEN
IAC #2 DRIVER CIRCUIT OPEN
IAC #3 DRIVER CIRCUIT OPEN
IAC #4 DRIVER CIRCUIT OPEN
POWERTRAIN CONTROL MODULE (IAC #1 DRIVER)
POWERTRAIN CONTROL MODULE (IAC #2 DRIVER)
POWERTRAIN CONTROL MODULE (IAC #3 DRIVER)
POWERTRAIN CONTROL MODULE (IAC #4 DRIVER)

P0122-THROTTLE POSITION SENSOR VOLTAGE LOW

Possible Causes

THROTTLE POSITION SENSOR SWEEP
INTERMITTENT CONDITION
5 VOLT SUPPLY CIRCUIT SHORTED TO GROUND
5 VOLT SUPPLY CIRCUIT OPEN
THROTTLE POSITION SENSOR INTERNAL FAILURE
THROTTLE POSITION SENSOR SIGNAL CIRCUIT SHORTED TO GROUND
THROTTLE POSITION SENSOR SIGNAL CIRCUIT SHORTED TO SENSOR GROUND CIRCUIT
TCM INTERNALLY SHORTED THROTTLE POSITION SIGNAL CIRCUIT
PCM 5 VOLT SUPPLY CIRCUIT
PCM THROTTLE POSITION SENSOR SIGNAL

 

Hi Guys, I'm working on this Cherokee with Carter54.

I want to bump this up with some more information. I took the advice and checked 5v suppply on a couple sensors and found 0v with the key on. This mad me check pin 17 on the pcm which should be +5v for all the sensors and it read 0v with the key in the on position. I then checked the 12v source to the pcm pin 23 or 22 and that read 12v.

I'm wondering what to do next. Are there some sensors I need to check to see if one is shorted to ground? Or should I just go buy a new pcm? I guess I need to figure out what is causing my 5v supply to be 0v.

Thanks

 

First, if you haven't checked yet, verify all the fuses in the passenger kick panel are good. There are a couple circuits there that can cause a crank/no start symptom.

Next, unplug all the sensors powered by the 5V supply. Disconnect the battery, turn the headlights on for a few second to drain off any residual voltage and then reconnect the battery. Check for you 5V supply from the PCM again. If it's not there with all the sensor unplugged then you either have a bad PCM or a short in the wiring.

Is it possible the rear end collision damaged any wires in the rear of the vehicle? Would be wise to check this also.