Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC P1129: MAP Sensor Signal Higher Than Expected
- Check for vacuum leaks in these parts.
- PCV valve
- PCV hose
- EVAP canister purge valve
- Throttle body
- Brake booster
- Brake booster hose
- Intake manifold
Are there any vacuum leaks?
YES -Repair or replace the part(s) with vacuum leaks, then go to step 9.
NO -Go to step 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.
- 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 5 seconds?
YES -Go to step 7.
NO -Go to step 4.
- Clear the DTC with the HDS.
- Test-drive under these conditions:
- Engine coolant temperature (ECT SENSOR 1) above 158°F (70°C)
- Transmission in 5th
- Vehicle speed between 55-75 mph (88- 121 km/h) for 10 seconds
- Vehicle speed decelerated with the throttle fully closed for at least 2 seconds or more
- 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.
- Turn the ignition switch to LOCK (0).
- Replace the MAP sensor (see MAP SENSOR REPLACEMENT ).
- Turn the ignition switch to ON (II).
- Reset the ECM with the HDS.
- Do the ECM idle learn procedure (see ECM IDLE LEARN PROCEDURE ).
- 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.
- Test-drive under these conditions:
- Engine coolant temperature (ECT SENSOR 1) above 158°F (70°C)
- Transmission in 5th
- Vehicle speed between 55-75 mph (88 - 121 km/h) for 10 seconds
- Vehicle speed decelerated with throttle fully closed for at least 2 seconds or more
- 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.
- 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.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.