XJ Burns out sensors like they are going out of style. - JeepForum.com
 
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post #1 of 3 Old 08-27-2014, 10:32 PM Thread Starter
Stargazer_84
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2001 XJ Cherokee 
 
Join Date: Aug 2014
Location: San Diego
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XJ Burns out sensors like they are going out of style.

Hey guys,

I know there are a ton of posts about CPS issues, I have read a bunch of them on here, but I believe this is a little different. I know that both my Crankshaft Position Sensor and my Camshaft Position Sensors are shorted out. I tested them, they failed, I replaced them with brand new Mopar parts and she ran beautifully for all of two days before the sensors burnt out again.

There has to be a short somewhere in the system that is burning out all of my sensors. I believe that there is something that is sending too much voltage through system, other wise how could brand new parts get internal shorts within days of being installed?

I am pretty sure it is either my PCM going bad or a short in the wiring harness that is blowing out all of my sensors. Is there any way for me to test which one? Also, I am getting the "no bus" in the gauges occasionally and my airbag light is on, and my battery is not charging but the alternator and battery test as good. I would hate to replace the PCM if it is just a short in the harness. But I'm not sure what to do.

Thanks

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post #2 of 3 Old 08-28-2014, 05:22 AM
BagusJeep
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1981 CJ7 
 
Join Date: Jul 2009
Location: Bali
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Both those sensors receive 8V supply from the PCM. You need to check at the sensor what the voltage is.

With the alternator you need to check the voltage on the engine at the post on the back with the engine running. 13.4 to 15V would be expected. If not then it may be the PCM controller, it gives the Field signal to the alternator.

Sounds like a general series of probems with the PCM. Have you taken apart and cleaned the connector and checked for corrosion and moisture?

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1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
1995 Cherokee 4.0 - CHEROKEE
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post #3 of 3 Old 08-28-2014, 06:04 AM
CCKen
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1999 XJ Cherokee 
 
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Several engine management sensors receive 5 volts from the PCM inorder to function.

The following receive the primary 5 volt supply:

Crankshaft Position Sensor. Camshaft Position Sensor, MAP Sensor, and Throttle Position Sensor. Each sensor receives the 5 volts via an Orange wire from the PCM.

You can determine if these sensors are receiving the proper voltage by using a digital voltmeter.

Unplug the TPS.

Turn the ignition switch to RUN (engine not started).

Touch the pin cavity of the sensor connector with the Orange wire with the meter + probe and the battery negative post with the - probe. you should see 5 +/- 0.5 volts.

If the voltage is higher than spec, repeat the test at the MAP sensor. If it too is high suspect the clockspring being at fault.

You can isolate the clockspring as the fault by removing the Junction Block fuse panel (in the passenger footwell) cover and removing the Horn Relay. The Horn Relay will be the center relay in the group of three relays you see.

Retest the voltage at the sensors you checked. If the voltage dropped to spec the clockspring is defective. Leave the Horn Relay out until such time as you can replace the clockspring.

If the voltage readings at the sensor connectors you checked the first time are within spec there's a problem elsewhere.

Do these things and get back.

Good luck.
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cps , No bus , pcm

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