DTC Troubleshooting

DTC Troubleshooting: P1129

DTC P1129: MAP Sensor Signal Higher Than Expected

NOTE: Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information. Initial Inspection and Diagnostic Overview

1. Check for vacuum leaks in these parts:
- PCV valve

- PCV hose

- EVAP canister purge valve

- Throttle body

- Intake manifold

- Brake booster

- Brake booster hose

Are there any vacuum leaks?
YES - Repair or replace parts with vacuum leaks, then go to step 9.

NO - Go to step 2.


2. Start the engine. Hold the engine speed at 3,000 rpm without load (in neutral) until the radiator fan comes on, then let it idle.

3. Check the MAP SENSOR in the DATA LIST with the HDS.

Is more than 36.9 kPa (11.0 in.Hg, 277 mmHg) or 1.1 V held for more than for 5 seconds?
YES - Go to step 7.

NO - Go to step 4.


4. Clear the DTC with the HDS.

5. Test-drive under these conditions:
- Engine coolant temperature (ECT SENSOR 1) above 158 °F (70 °C)

- Transmission in 5th

- Drive at a steady speed between 55-75 mph (88-120 km/h) for 10 seconds

- During the drive, decelerate (with throttle fully closed) for at least 2 seconds

6. Monitor the OBD STATUS for DTC P1129 in the DTCs MENU with the HDS.

Does the screen indicate FAILED?
YES - Go to step 7.

NO - If the screen indicates PASSED, intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at the MAP sensor and the ECM. If the screen indicates NOT COMPLETED, go to step 5 and recheck.


7. Turn the ignition switch to LOCK (0).

8. Replace the MAP sensor. Service and Repair

9. Turn the ignition switch to ON (II).

10. Reset the ECM with the HDS.

11. Do the ECM idle learn procedure. ECM Idle Learn Procedure

12. Start the engine. Hold the engine speed at 3,000 rpm without load (in neutral) until the radiator fan comes on, then let it idle.

13. Test-drive under these conditions:
- Engine coolant temperature (ECT SENSOR 1) above 158 °F (70 °C)

- Transmission in 5th

- Drive at a steady speed between 55-75 mph (88-120 km/h) for 10 seconds

- During the drive, decelerate (with throttle fully closed) for at least 2 seconds

14. Check for Temporary DTCs or DTCs with the HDS.

Is DTC P1129 indicated?
YES - Check for poor connections or loose terminals at the MAP sensor and the ECM, then go to step 1.

NO - Go to step 15.


15. Monitor the OBD STATUS for DTC P1129 in the DTCs MENU with the HDS.

Does the screen indicate PASSED?
YES - Troubleshooting is complete. If any other Temporary DTCs or DTCs were indicated in step 14, go to the indicated DTC's troubleshooting.

NO - If the screen indicates FAILED, check for poor connections or loose terminals at the MAP sensor and the ECM, then go to step 1. If the screen indicates NOT COMPLETED, go to step 12.