The P1129 Honda OBDII Trouble Code is caused by your PCM receiving too high of a signal from the Manifold Absolute Pressure Sensor. This can also be caused if your vehicle has a problem with an external Barometric Pressure Sensor.
Today, I will be showing you how to correct the P1129 Honda code on a 1996 Honda Civic EX D16y8. This Circuit High Input error can be caused by a faulty MAP sensor or short in engine wiring.
What does the OBDII DTC P1129 Honda trouble code Mean? – This check engine trouble code is most frequently related to a failure of your Manifold Absolute Pressure sensor. This could include but is not limited to wiring, the sensor or any supporting device.
What needs to be tested for the
P1129 Honda trouble code?
The 1.6L SOHC Honda Engine utilizes a three wire sensor that translates the incoming intake charge into a voltage that the PCM can understand. When your sensor is faulty or there’s another issue with your wiring, your PCM can read too high of a signal, triggering the
P1129 Honda Check Engine Code.
Today we’ll be showing you how to test, service and replace the MAP sensor in a 1997 Honda Civic EX. This walkthrough will show you the step by step breakdown on what to do when your MAP sensor needs service.
Where is the MAP Sensor located?
The D16y8 MAP sensor is mounted onto the throttle body assembly, adjacent to the throttle position sensor. Because of the similarity with the plug design and wiring, people often mix up the MAP and TPS on Honda engines.
To reach the MAP sensor on our 1997 Honda Civic EX, we will need to remove the intake snorkel and airbox to gain access.
You will need a flathead screwdriver along with socket and 10mm socket with accompanying ratchet. This DIY HP1129 Honda How To also involves the use of a voltmeter or similar testing device that allows you to measure at the wire.
Unplug your two pin air intake temperature connector located on the right side of your factory air filter housing. Pull off the top of your housing by unclipping the metal bands that hold the housing together.
Lift the top of the air intake filter housing off and you can bend the intake snorkel to rest it elsewhere in your engine bay. You do not need to undo or remove the rest of your air intake snorkel.
The vacuum hose shown above must be removed before the lower portion of your intake filter housing can be removed. Undo the metal clips here and slide them down to remove the rubber hose.
You are now ready to remove the 8mm bolt that holds the lower intake housing in place.
With the lower intake housing removed from your D16Y8, you can now reach your Manifold Absolute Pressure sensor. Failure of this sensor and its function is primarily the driving force behind the P1129 Honda check engine code.
Unplug this electrical connector to identify the wires and colors you will be working with. The entire process of how to fix your Honda Civic MAP sensor is much easier if you know what colors do what before you begin testing.
Turn your ignition to the “ON” position so that your MAP sensor is powered, but do not start your Honda Civic. Check wire 1 on the three pin MAP connector for power by putting the black lead of your voltmeter to ground, and testing the back of your MAP connector with the yellow with red stripe wire.
You can use a paper clip or a needle to make contact with the metal contact of the harness through the back of the connector. Many times when you have a P1129 Honda error code, the cause can be from a loose connector or damage to the wires leading to the sensor.
You should see this wire send a 5v sensor power with the key at the “ON” position, if so move to testing the MAP sensor ground. If you do not have 5 volts of power at this stage, double check that the key is at the “ON” position.
If there’s still no power here, you have a short somewhere in the wiring harness. You will either need to find the break in your wiring harness professionally, or run a separate wire from your P2P Honda ECU to power the MAP sensor.
Check our How To Check for Wiring Breaks or How To Wire a Sensor from your ECU article for further information.
Testing the MAP sensor ground
If you have power at your MAP sensor, now you will be using your voltmeter to test the middle pin or green wire with white stripe for chassis ground. Connect the red lead of your voltmeter to the positive terminal of your battery and backprobe the middle wire. You should find ground here, if not you can elect to run a seperate wire to your P2P Honda ECU and ground the MAP sensor. If you do not have a ground signal here your MAP sensor will not be powered, thus triggering your P1129 OBDII code.
Testing the MAP sensor signal
Now using the positive terminal on your voltmeter, measure the MAP sensor signal wire on your connector with the key in the “ON” position. You should see a value below the 1.0 volt value at idle. If you do see this voltage, try disconnecting your MAP sensor by unscrewing the two screws that hold it in place.
Leave the MAP sensor connected and gently blow into it with an air compressor, remember you don’t need 50 psi here just enough to make the MAP sensor register. Your Honda MAP sensor will not read anything above .8 bar or 11psi so make sure you keep it low.
You should see a gradual, linear curve to the MAP voltage with this method. The voltage should not jump or have any obvious gaps in it and should definitely peak at 11psi. If your MAP sensor voltage falls outside of these specifications, it could be time to replace your MAP sensor.
Have any questions about this guide on testing your MAP sensor and fixing the P1129 Honda OBDII trouble code? Leave me a message below and let me know!