Q: car won't start and keeps showing error code P0129.

asked by on

After replacing a faulty clutch pressure plate in my 2004 pt cruiser (base not turbo), I attempted to start the engine. The engine would not kick over and the check engine light kept flashing. I checked the codes and it was showing a bad cam shaft sensor and a faulty barometric sensor. I replaced both sensors and cleared both codes. After replacing both sensors the car still won't start and is continuing to show the code P0129. Any ideas as to what the problem could be?

My car has 105550 miles.
My car has a manual transmission.

With a reoccurring code such as this, after replacing the sensor, it is time to test the wiring harness and connector at the sensor. The orange wire should have 5V. This would be the 5 volt reference. The black and light blue wire is the ground and the dark green and red wire is the MAP sensor signal the is returned to the PCM through the sensor. This code indicates the voltage from the MAP sensor to the PCM is greater than 4.9 volts or less than 2.28 volts. When this occurs, there is usually a short to ground or a short to power. You will need to check the voltage on the dk grn/red wire to know which it is.

A problem like this will often affect all or more than one sensor with that uses the 5V reference. If you find the 5V reference is high or low, it is often necessary to disconnect each sensor that uses the 5V reference while monitoring the reference signal. When the signal changes back to 5v and not above 4.9 or below 2.28 volts, you have found the bad sensor.

If once you have checked all of this you have not found the source of the short to ground or power, it is time to suspect the PCM. You will want to check the 5v reference, grounds and power pins directly at the PCM by back probing at the PCM connector.

This can be quite an undertaking to diagnose such a problem. If you lucky, you will find a wire that is broken or something along those lines. If you should require further assistance with this, I recommend the following inspection; Car is not starting inspection.

Good luck!

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. car won't start and keeps showing error code P0129.

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Codes P0129 and P0175.

Hello. Thank you for writing in. With the codes you are receiving, and due to the order in which they triggered, you will want to focus on the P0129 MAP sensor reading. The Manifold Absolute Pressure sensor uses a 5...

Q: My Toyota windom is not starting.

Hi there. Check the battery cables to see if they are are tight and clean. If the cables are loose or corroded, then clean them and tighten them up. If the cables are fine, then check the battery voltage and...

Q: Check engine light signal on a 2005 PT Cruiser

Two possible reasons for the light include an issue with the transmission or a faulty fuel/air ratio. There are over 2000 different codes for that Check Engine Light so you will need to get it scanned. If you want have...

Related articles

P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...