Tech Tip: Intermittent No-Start on Ford 5.4L V8 Truck Engine

Tech Tip: Intermittent No-Start on Ford 5.4L V8 Truck Engine

When it won't start, there is no communication with the Powertrain Control Module (PCM). The theft light is flashing rapidly with codes U1147 and U1262 in the Hybrid Electronic Cluster (HEC). Also, the odometer just shows dashes with the key on instead of the actual mileage.

Vehicle Applications: 1999 Ford E-250 Econoline 5.4L, GAS, Vin L, Eng Cfg V8; and 1999 Ford F-150 5.4L, GAS, Vin L, Eng Cfg V8.

Customer Concern: Intermittent no start.

When it won’t start, there is no communication with the Powertrain Control Module (PCM). The theft light is flashing rapidly with codes U1147 and U1262 in the Hybrid Electronic Cluster (HEC). Also, the odometer just shows dashes with the key on instead of the actual mileage.

Potential Causes: Shorted Harness; PCM; Shorted Sensor.

Tech Tips: If the PCM is at fault, a factory scanner or equivalent will be needed to configure the PATS for the new PCM.

Diagnostic Codes: U1147, U1262.

Tests/Procedures
1. Check for battery voltage to the PCM on pins 71 and 97 red wires with key on. Check pins 25 light blue/yellow (LB/YE) wire, 3, 51, 77 and 103 black/white (BK/WH) wires for good ground. If OK, check for 5V reference voltage on pin 90 brown/white (BR/WH) wire with the PCM connected and key on.

2. If the Reference Voltage (VREF) is low, disconnect the Differential Pressure Feedback EGR (DPFE) Sensor, Throttle Position Sensor (TPS) and Fuel Tank Pressure (FTP) sensor one at a time to see if the voltage returns. If not, cut the BR/WH wire near the PCM or remove the wire from the PCM connector and recheck on the PCM side to see if the voltage returns. If so, check for a short to ground in the harness.

3. If the voltage out of the PCM on pin 90 is still low with the harness and sensors eliminated, but the powers and grounds are OK, replace the PCM.

4. If the powers and grounds and VREF are all OK, but the PCM will not communicate, verify the tan/orange (TN/OG) wire is not open between pin 16 of the PCM connector and pin 2 of the DLC. Also check the pink/light blue (PK/LB) wire from pin 15 of the PCM to pin 10 of the DLC making sure the wire is not open. If all wires are OK, replace the PCM and recheck operation.

Courtesy of Identifix, Inc.

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