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  #1  
Old 05-23-2009, 09:44 PM
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Join Date: Jun 2008
Location: Clinton, Ct
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A pair of error codes (P0120 & P0380)

My 96 e300d keeps me busy with GREMLIN type problems and the latest is a “check engine” light that when checked displays two codes. The first is a “ P0120 - Throttle Position Sensor/Switch A Circuit Malfunction” and the second is “P0380 - for Glow plug circuit A failure”. The “check engine” light comes on and stays on for a day or two then goes off. The car operates fine light on or off. I know that I should replace the glow plug harness based on inspection (cracked insulation at plug connections).

Has anyone else experienced this problem and what was done to fix it? Could the pair of faults be related?
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  #2  
Old 05-23-2009, 11:42 PM
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Join Date: Jul 2007
Location: USA
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your tps may be going. A bad tps will cause the car to stall. Since your car isnt stalling yet good chance it will eventually will. also check the circuitry to the tps. The check engine will normally go out after some time and the error code and data will be stored in the pcm memory until its cleared.
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  #3  
Old 05-24-2009, 12:53 AM
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Location: Walnut Creek, CA (one day 60°52'53.93"N, 150°49'39.24"W)
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For PO 380 you should check resistance of the GP's and confirm the relay is working. The code trips when the ECU registers that a start was attempted on one or more cold GP's.

That code is MOST often caused by user error.

If a cold start doesnt occur again within 3 cold, hot, cold run cycles the light resets itself.
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  #4  
Old 05-24-2009, 09:52 AM
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Join Date: May 2007
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[QUOTE=ctsailor;2207412][COLOR=black][FONT=Arial][SIZE=3]My 96 e300d keeps me busy with GREMLIN type problems and the latest is a “check engine” light that when checked displays two codes. The first is a “ P0120 - Throttle Position Sensor/Switch A Circuit Malfunction” and the second is “P0380 - for Glow plug circuit A failure”. The “check engine” light comes on and stays on for a day or two then goes off. The car operates fine light on or off. I know that I should replace the glow plug harness based on inspection (cracked insulation at plug connections).

As far as the glow plug circuit failure, you may have either a bad plug, or as you mention faulty wiring. The Throttle Position Sensor code can be a little tricky to pin down. Last summer, while on vacation, my vehicle threw the same TPS code, with no driving issues to speak of. After getting home, and going on the forum, I read some excellent posts regarding that particular code. The TPS code can be thrown if any sensor in that circuit is faulty or not functioning as designed. The circuit consists of the Throttle Position sensor, then the small sensor that is connected by a small black hose coming off the intake manifold, and two other sensors (same part number) located on the side of the air filter box. One of those sensors operates the EGR valve, the other the resonance flaps. In my case, I inspected all the vacuum lines leading to each sensor and resonance control valve to insure there were no leaks. Then I removed each electrical connection plug and sprayed it with electrical contact cleaner, and reconnected them. Once having done that, I cleared the code, and it has not returned in over a year. Hope yours is as easy to fix as mine turned out to be.
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  #5  
Old 05-24-2009, 12:11 PM
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Location: Clinton, Ct
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Thanks for the replys. I have done a lot of reading about the p0380 error and have a plan of action including a new harness.

I now also have a plan of action for the p0120 but dont want to replace the TPS because its part of a very expensive part. I will do the checking hope to find a bad vacuum line otherwise.....I love the car but hate the problems.

thanks again
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