Diagnostic Aids

Perform this test when instructed during QUICK TEST or if directed by other test procedures. Some vehicles may not have power steering, but PCM may be equipped with PSP switch software strategy. If a KOEO DTC P1650 or P1651 is displayed, check if vehicle is equipped with power steering. If vehicle is not equipped with power steering, disregard DTC P1650 or P1651. This test is only intended to diagnose.

Wiring Harness Circuits (SIG RTN & PSP)
PSP Switch
Powertrain Control Module (PCM)

Fig 1: Identifying PSP Switch Circuits & Connector Terminals (Contour & Mystique)

Courtesy of FORD MOTOR CO.

Fig 2: Identifying PSP Switch Circuits & Connector Terminals (Focus)

Courtesy of FORD MOTOR CO.

Fig 3: Identifying PSP Switch Circuits & Connector Terminals (Except Contour, Focus & Mystique)

Courtesy of FORD MOTOR CO.

1) DTC P1650: Verify Electrical Function

DTC P1650 indicates PSP signal is out of self-test range. Possible causes for these faults are:
- Open Or Short In Wiring Harness
- Faulty PSP Switch
- Faulty PSP Switch/Shorting Bar Damage
- Faulty Powertrain Control Module (PCM)
Start engine and allow to idle. Using scan tool, select PSP PID (PSP V PID on Sable and Taurus) from PID/DATA MONITOR & RECORD menu. Observe PID and turn steering wheel left, then right. If PID value does not indicate a change, go to next step. If PID value indicates a change, go to step 10).

2) Check PSP Switch Operation

Turn ignition switch to OFF position. Disconnect PSP switch connector. Install a jumper wire between PSP switch harness connector terminals. Start engine and allow to idle. Record PID reading. Disconnect jumper wire and record PID reading. On Sable and Taurus, if PSP V PID changed from less than one volt to more than 8 volts, replace PSP switch. On all models except Sable and Taurus, if PSP PID changed from high to low, replace PSP switch. On all models, if PID value did not change as specified, go to next step.

3) Check PSP Circuit Resistance

Turn ignition switch to OFF position. Disconnect PCM connector(s). Inspect connector for loose, damaged or corroded terminals. Repair as necessary. On LS, measure resistance of PSP circuit between PCM connector terminal A37 and PSP terminal at PSP switch harness connector. On all other models, measure resistance of PSP circuit between PCM connector terminal No. 31 and PSP terminal at PSP switch harness connector. See Fig 1-Fig 3 . On LS, measure resistance of SIG RTN circuit between PCM connector terminal A17 and SIG RTN terminal at PSP switch harness connector. On all other models, measure resistance of SIG RTN circuit between PCM connector terminal No. 91 and SIG RTN terminal at PSP switch harness connector. If both resistance readings are less than 5 ohms, go to next step. If any resistance reading is 5 ohms or more, repair open in PSP or SIG RTN circuit.

4) Check For Short In PSP Circuit

On LS, measure resistance between PCM connector terminals No. A37 and A17. On all other models, measure resistance between PCM connector terminals No. 31 and 91. On LS, measure resistance between PCM connector terminal A37 and chassis ground. On all other models, measure resistance between PCM connector terminal No. 31 and chassis ground. If both resistance readings are 10 k/ohms or more, replace PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Program PCM. See FLASH VEHICLE IDENTIFICATION BLOCK PROCEDURE . If any resistance reading is less than 10 k/ohms, repair short circuit.
NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 4) to step 10). No test procedures have been omitted.

10) DTC P1651: Check PSP Circuits For Intermittent

DTC P1651 can be set by towing vehicle with engine running or if a power steering concern was present. P1651 indicates PSP signal malfunction. Possible causes for these faults are:
- Open Or Short In Wiring Harness
- Faulty PSP Switch
- Faulty PSP Switch/Shorting Bar Damage
- Faulty Powertrain Control Module (PCM)
Turn ignition switch to ON position. Using scan tool, select PSP PID (PSP V PID on Sable and Taurus) from PID/DATA MONITOR & RECORD menu. While observing PSP PID, lightly tap on PSP sensor to simulate road shock. Wiggle sensor connector. Wiggle and bend circuits between PSP sensor and PCM. A fault is indicated by a sudden change of PSP PID voltage. If no fault is indicated, turn ignition switch to OFF position and reconnect PSP sensor connector, go to TEST Z . If fault is indicated, isolate area and repair as necessary.