DTC Troubleshooting

DTC Troubleshooting: P1128

DTC P1128: MAP Sensor Signal Lower 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. Inspect the air cleaner element. Service and Repair

Is it OK?
YES - Go to step 2.

NO - Clean or replace the air cleaner element. Service and Repair


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

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

Is there less than 54.1 kPa (16.0 in.Hg, 406 mmHg) or 1.61 V held for more than 5 seconds?
YES - Go to step 8.

NO - Go to step 4.


4. Clear the DTC with the HDS.

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

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

- Engine speed between 1,200-5,500 rpm

- Transmission in D position

- Vehicle speed accelerated from 16-31 mph (25-50 km/h) under half throttle

7. Monitor the OBD STATUS for DTC P1128 in the DTCs MENU with the HDS.

Does the screen indicate FAILED?
YES - Go to step 8.

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 PCM. If the screen indicates NOT COMPLETED, go to step 5 and recheck.


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

9. Replace the MAP sensor. Service and Repair

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

11. Reset the PCM with the HDS.

12. Do the PCM idle learn procedure. PCM Idle Learn Procedure

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

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

- Engine speed between 1,200-5,500 rpm

- Transmission in D position

- Vehicle speed accelerated from 16-31 mph (25-50 km/h) under half throttle

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

Is DTC P1128 indicated?
YES - Check for poor connections or loose terminals at the MAP sensor and the PCM, then go to step 1.

NO - Go to step 16.


16. Monitor the OBD STATUS for DTC P1128 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 15, 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 PCM, then go to step 1. If the screen indicates NOT COMPLETED, go to step 14.