Spark

DTC P1391

The engine control module (ECM) identifies engine misfire by detecting variations in crankshaft speed. Crankshaft speed variations can also occur when a vehicle is operating over a rough road. The ECM receives a rough road signal by a rough road sensor or an electronic brake control module (EBCM), if equipped with the antilock brake system (ABS). The ABS can detect if the vehicle is on the rough surface based on wheel acceleration/deceleration data supplied by each wheel speed sensor. This information is sent to the ECM by the EBCM through the rough road signal circuit. For vehicles without ABS, the ECM receives a rough road signal from a wheel speed sensor located at the front left wheel. The ECM can determine if the vehicle is on a rough road surface based on the signal from the wheel speed sensor.

The ECM detects that the change in rough road wheel speed sensor signal is less than 2 km/h (1.2 mph) while the change in vehicle speed is greater than 5 km/h (3.1 mph).

DTC P1391 is a Type C DTC.

DTC P1391 is a Type C DTC.

Schematic Reference

Engine Controls Schematics : Siemens ECM - LPG with LCP → Siemens ECM - Gas without FX3 or LCP → Delphi ECM - FX3

Connector End View Reference

Component Connector End Views

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information.

1. Observe the DTC information with a scan tool. DTC P1391 should not set.
2. Operate the vehicle within the conditions for running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

1. Ignition OFF, disconnect the harness connector at the B171 Rough Road Sensor.
2. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 2 and ground.

⇒	If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test all components connected to the ignition circuit and replace as necessary.

3. Ignition ON, test for 0.2-0.8 V between the signal circuit terminal 1 and ground.

⇒	If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K20 ECM.

⇒	If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the K20 ECM.

4. If all circuits test normal, replace the B171 Rough Road Sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.