Diagnostic Aids

Perform this test only when directed here. This system test is intended to diagnose:

• PTO wiring harness circuit. See Fig 1.
• Powertrain Control Module (PCM).

Fig 1: Identifying PTO Circuit & Switch Schematic

Courtesy of FORD MOTOR CO.

1. 1) Check PTO Switch
   
   PTO signals PCM that additional load is being applied to engine. If PTO circuit failure occurs, a DTC may be set. Possible causes for this fault are:
   • PTO circuit shorted to power.
   • Faulty Powertrain Control Module (PCM).

   Turn ignition off. Disconnect PTO switch connector. Measure resistance between PTO switch terminals. With switch off, resistance should be more than 10,000 ohms. With switch on, resistance should be less than 5 ohms. If resistance is as specified, go to next step. If resistance is not as specified, replace PTO switch. Perform OBD-II DRIVE CYCLE. See DRIVE CYCLES  under ADDITIONAL SYSTEM FUNCTIONS.

2. 2) Check For Short To Power
   
   Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Turn ignition on. Measure voltage between PCM connector pin No. 4 and negative battery terminal. If voltage is less than one volt, reconnect PCM and PTO switch connectors and go to next step. If voltage is one volt or more, repair circuit short to power.
3. 3) MIL On: Check PTO PID
   
   Turn ignition off. Connect scan tool to DLC. Turn ignition on. Using scan tool, select PTO PID from PID/DATA monitor.
   NOTE: Some vehicles do not support a PTO PID.

   If PTO PID is available and displaying ON or OFF, go to next step. If PTO PID is not as specified, go to step  9).

NOTE: The following step requires operating PTO. Refer to PTO manufacturer operating manual for operating instructions.
4. 4) Check PTO Circuit With Scan Tool
   Turn ignition on. Engine may need to be started to engage PTO. Cycle PTO switch/handle while observing PTO PID. If PID cycled ON, delay, then turned ON, PTO input is okay. Check for additional symptoms and repair as necessary. If PID value is not as specified, go to next step.
5. 5) Check PTO Circuit For Short To Ground
   
   Turn ignition off. Disconnect PCM 104-pin connector. Disconnect PTO switch connector. Disconnect scan tool from Data Link Connector (DLC). Measure resistance between PCM connector pin No. 4 and negative battery terminal. If resistance is 10,000 ohms or less, repair short circuit. If resistance is more than 10,000 ohms, go to next step.
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 5) to step 7). No test procedures have been omitted.
6. 7) Check PTO PID Value
   
   Reconnect PCM connector. Connect scan tool to DLC. Connect a jumper wire between positive battery terminal and PTO terminal at PTO switch wiring harness connector. Turn ignition on. Using scan tool, select PTO PID. PID value should be ON with jumper wire and OFF with jumper wire disconnected. If PID value is as specified, PTO circuit from PTO switch to PCM is okay. Refer to PTO manufacturer for service information of PTO. If PID value is not as specified, go to next step.
7. 8) Check Circuit Resistance
   
   Turn ignition off. Disconnect PCM connector. Measure resistance between PCM connector pin No. 4 and PTO terminal at PTO switch wiring harness connector. If resistance is less than 5 ohms, replace PCM. If resistance is 5 ohms or more, repair open in PTO circuit.
8. 9) Perform KOEO & KOER Self-Test
   
   Perform KOEO ON-DEMAND SELF-TEST  and KOER ON-DEMAND SELF-TEST  . If any DTCs are present, service DTCs as necessary. If no DTCs are present, go to next step.
9. 10) Perform Drive Cycle
   
   Ensure PTO is disengaged. Perform OBD-II DRIVE CYCLE. See DRIVE CYCLES  under ADDITIONAL SYSTEM FUNCTIONS. Retrieve Continuous Memory DTCs. If any DTCs are present, service DTCs as necessary. If no DTCs are present, fault cannot be duplicated at this time. MIL on can be caused by engaging PTO, creating an engine load while OBD-II monitors were running. If symptom is still present, go to TEST Z .