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 and PSP).
• PSP switch.
• Powertrain Control Module (PCM).

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

Courtesy of FORD MOTOR CO.

Fig 2: Identifying PSP Switch Circuits & Connector Terminals (Except Contour, Cougar & Mystique)

Courtesy of FORD MOTOR CO.

1. 1) DTC P1650 Or P1651
   
   DTC P1650 indicates PSP signal is out of self-test range. DTC 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).

   Start engine and allow to idle. Using scan tool, select PSP PID (PSP V PID on Sable and Taurus) from PID/DATA monitor 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, unable to duplicate or identify fault. Go to TEST Z .

2. 2) Check PSP Switch Operation
   
   Turn ignition off. Disconnect PSP switch connector. Install a jumper wire between PSP switch wiring 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 zero volts to 3.8 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. 3) Check PSP Circuit Resistance
   
   Turn ignition off. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Measure resistance of PSP circuit between PCM connector pin No. 31 and PSP terminal at PSP switch wiring harness connector. Also measure resistance of SIG RTN circuit between PCM connector pin No. 91 and SIG RTN terminal at PSP switch wiring 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. 4) Check For Short In PSP Circuit
   
   Measure resistance between PCM connector pins No. 31 and 91. Also measure resistance between PCM connector pin No. 31 and chassis ground. If both resistance readings are 10,000 ohms or more, replace PCM. If any resistance reading is less than 10,000 ohms, repair short circuit.