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

asked by on November 11, 2016

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.

Car is not starting Inspection $79.99 - $89.99 Get a Quote

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!

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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

What others are asking

My car won't start when I turn the key, I have to press on gas for it to start

Hi there. It sounds like a coincidence that it started when the gas pedal was pressed. The most common issue on the Mazda 6 is the key itself. If the computer does not pick it up correctly, then it will...

Changed catalytic converter, no lights on dashboard, but codes for catalytic converter & O2 sensor still remain

Hello. If you have changed these parts and if the check engine light is not on but the codes remain then you should drive the vehicle for a while. it can take about 500 miles for them to clear. If...

My driver's side headlight won't turn on and a new bulb didn't fix it

Your vehicle has a recall on the headlight wiring connectors and bulbs. If the connectors do not have a made in Mexico tag on them, then they will need to be replaced with new bulbs and connectors as per recall...

chrysler 2012 200,horn does not honk when you lock it with the remote

First check the vehicle settings. If you have a Menu button on the steering wheel, follow these instructions: Press and release the MENU button until “Personal Settings” displays. Press and release the DOWN button to display the following programmable features:Sound...

Can I use fuel line repair kit for fuel line leak?

Possibly. The repair kits and fittings being vended in the aftermarket have different applications, in particular low pressure return versus high pressure supply from the fuel pump. If both ends of the OEM tube presently on the vehicle are accessible...

Electrical problems in the dashboard

With this many problems, I suggest having a qualified technician perform a full vehicle inspection and diagnostic to see what repairs need immediate attention and which issues can wait. With these symptoms, it would probably not be best to drive...

my car won't start

This can happen for a wide variety of reasons. Unfortunately, without additional detail this cannot be diagnosed properly without inspecting the car. I would recommend having a certified expert, such as one from YourMechanic, come to your home to diagnose...

Significant gas mileage drop after tire change

If the vehicle fuel efficiency has dropped 15%, and there is no obvious explanation, something is wrong. The timing of the tire replacement to the drop-off in mileage is undoubtedly just a coincidence unless the tires are wildly defective thus...

truck wont go into drive but will go into reverse

You should first see if the transmission shifter is moving through all the gears by the gear shifter and the cable and connections are okay. Then make sure the fluid is full. If all this checks out, then you may...

Related articles

Symptoms of a Bad or Failing Flexible Clutch Hose
Common signs include difficulty shifting, low clutch fluid, and feeling no resistance at the clutch pedal.
Chrysler Certified Pre-Owned (CPO) Car Program
If If you are shopping for a used Chrysler vehicle, you may want to check out cars under their certified pre-owned program. Many manufacturers have a certified pre-owned (CPO) program, and each one is set up differently. Read on to...
A Buyer’s Guide to the 2012 Chrysler 200
In In 2011, Chrysler completely overhauled, updated, and remodeled their entire line, including the introduction of the new Chrysler 200. This reimagining of the old, boring Dodge Sebring sedan was already an exciting move for Chrysler, and the 2012 Chrysler...