XJ Wrong PCM replacement? No spark

Yes on both the ASD and ASD relay fuse

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Use the OBD-II trouble codes to guide your diagnostics and sensor testing.

A simple Google search discovers this:


P0122 JEEP - Throttle Position Sensor/Accelerator Position Pedal Circuit Low Input

Possible causes
•Faulty throttle position sensor
•Throttle position sensor harness is open or shorted
•Throttle position sensor circuit poor electrical connection
•Faulty Powertrain Control Module (PCM)



P1694 JEEP - No Messages Received From The Powertrain Control Module

Possible causes
•CCD Bus (-) circuit open between Powertrain Control Module (PCM) and Transmission Control Module (TCM)
•CCD Bus (+) circuit open between PCM and TCM
•Transmission CCD bus wiring damaged
•Faulty TCM

I feel like I am chasing my tail here.....or maybe making headway. Not sure. I have been able to get rid of the last two fault code by replacing a couple of parts thanks to everyone's help. However now I have a new code. Not sure if fixing the last codes allows the computer to see a new faulty sensor or not. I have a replacement camshaft position sensor on the way as that is the new error code. Could this be because the Jeep was sitting for two years or am I just chasing my tail here?

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A possibility is you have a sensor on the 5 V supply tree (orange wire) that has low resistance or is partially shorted. If the 5 V orange wire supply voltage is low it can cause a bus error.

One way to check (low tech) is to hook up a voltmeter to the orange wire at a good easily accessible position and unplug the sensors on the 5 V orange wire tree. I'd start with the sync (cam position sensor) then the TPS, then the MAP and then the oil pressure sensor, When the right sensor is unplugged the voltage in the 5 volt supply will come back up and hopefully, the bus error will disappear.

Check that the wires for the oil pressure sensor aren't chaffed and/or contacting ground, a known trouble spot.

I had a CPS that tested good but wasn't, it was sucking down the voltage in the 5 V supply orange wire tree. On a hunch I unplugged the CPS and my bus came back. Could be another sensor doing the same thing.

I'd check the cheap stuff before I'd do the expensive stuff. My standard troubleshooting routine is to test easy then hard, cheap then expensive.

I agree that probing for 5 volts at all the OBD sensor is a good starting point. Physically look for wire harness damage and wire plug damage and consider that there may be one or more faulty wire splices.


P0340 JEEP - Camshaft Position Sensor

P0340 Jeep Possible Causes:
•Faulty Camshaft Position Sensor
•Camshaft Position Sensor wire harness is open or shorted
•Camshaft Position Sensor wire plug poor electrical connection
•Faulty starter motor
•Starting system circuit
•Dead (Weak) battery

P0340 Jeep Tech Notes:
Sometimes and in some models, low battery voltage or a weak starter can trigger a Camshaft Position Sensor code.

Okay thanks guys. I have a new camshaft position sensor on its way and should be here mid next week. I will check to make sure the wires are not all jacked us as well, that doesn't cost a dime so that is easy. I think I need to find a local junkyard that I can get spare parts at for this thing. LOL

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All three of my Cherokees carry a spare Crank and Cam sensor.

Okay so my Bluetooth obd2 died on me but I have a new one now. I changed both the cam shaft and crank shaft sensors and I am still getting the P0340 error. I am getting my self a bit confused though. Which sensor should I be looking for 5volts on?

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All of the OBD-II engine control sensors are 5 volts.

Well that makes it easy. Thanks.

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So I have check for 5volts and I have around 5.1 at each sensor. I have replaces the battery with a know good battery. All of the wireing is in factory plastic conduit and did not pull it apart but I checked all the connections for corrosion and gave then a tug at the sensors to see if anything pulled apart. The fault code is still there and will still not fire. I have ordered another CPS thinking that maybe the new one was faulty. Plus you can never have to many spares. I am also ordering a replacement starter. Is is possible that the ECU that I purchased is to blame? I know there was mention of a possible imobilizer. How can I figure out if this Jeep has one?

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Are you installing genuine Jeep OBD sensors or cheap crappy Chinese clone sensors ?

If the Cherokee has the factory installed Sentry Key Immobilizer System (SKIM) anti-theft, the chip-in-key reader device is at the ignition cylinder, and the chipped keys are typically light gray. If the Cherokee has some sort of aftermarket anti-theft, you will need to search for in the dash.

Refurbished ECU have a very high defect and failure rate.

Have you performed a wire continuity test between all the OBD sensors and the ECU ?



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Yeah you are correct and I may be learning a valuable lesson here. They are shipping from USA but are not OEM. Sure the are crap. I guess I should head over to Napa today and buy a good one.

As for the imobilizer it does not appear that this Jeep has a factory one and I took a photo just to make sure someone does not see something that I missed. I am going to check for an after market one today.

Any idea where I can get a wiring diagram for this jeep to check for continuity to the sensors?

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On the ECU it was a use OEM on eBay. The seller stated it was not refurbished and was working when pulled.

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Genuine Jeep Service Manuals are $ 7.95 from www.pacificmanuals.com

The only way I know how to test an ECU is to substitute it with a known good working ECU.

Success. The cheap camshaft position sensor I bought on eBay was crap. Picked a new one from Napa and it started right up. What a waste of time and money. Lesson learned.

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Most auto parts stores ( and eBay/Amazon ) sell cheap crappy Chinese made parts, some that even come with a "Lifetime Warranty". These parts are poorly manufactured and/or made from inferior materials. They are often out of specification, or even failed, right out of the box. The ones that are not faulty many times will have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep engine sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts.

Cheap parts are cheap for a reason.