Diagnostic Aids

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

• PTO Wiring Harness Circuit.
• Powertrain Control Module (PCM)

Fig 1: Identifying PTO Circuit & Switch Schematic

Courtesy of FORD MOTOR CO.

1. 1) PTO PID Does Not Cycle: Check For Defective 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 In Aftermarket Switch Or VPWR
   • Faulty Powertrain Control Module (PCM)

   Turn ignition switch to OFF position. Disconnect PTO switch harness connector. Using a DVOM, measure resistance between PTO switch terminals. See Fig 1. With switch off, resistance should be more than 10 k/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 DRIVE CYCLE PROCEDURES under ADDITIONAL SYSTEM FUNCTIONS. Ensure OBD-II DRIVE CYCLE PROCEDURES are performed to verify repair.

2. 2) Check PTO Circuit For Short To VPWR
   
   Disconnect PCM connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Turn ignition switch to ON position. Using a DVOM, measure voltage between PCM harness connector terminal No. 4 and negative battery terminal. If voltage is less than one volt, reconnect PCM and PTO switch connectors and go to step  4). If voltage is one volt or more, repair circuit short to VPWR.
NOTE: Diagnostic steps  3)- 10) are performed when directed here from SYMPTOMS in TROUBLE SHOOTING - NO CODES - EEC-V - CNG & GASOLINE article.
3. 3) MIL On: Check PTO PID
   Possible causes for this fault are:
   • PTO Circuit Open
   • Short To Chassis Ground In PTO Circuit

   Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC). Turn ignition switch to ON position. Using scan tool, select PTO PID from PID/DATA MONITOR & RECORD. If PTO PID is available and displaying ON or OFF, go to step  1). 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 switch to ON position. Engine may need to be started to engage PTO. Cycle PTO switch/handle while observing PTO PID. If PTO PID cycles ON, delays, then turns OFF, diagnose by symptom and repair as necessary. Go to SYMPTOMS in TROUBLE SHOOTING - NO CODES - EEC-V - CNG & GASOLINE article. If PTO PID value does not cycle as specified, go to next step.
5. 5) Check PTO Circuit For Short To Ground
   
   Turn ignition switch to OFF position. Disconnect PCM connector. Disconnect PTO switch connector. Disconnect scan tool from DLC. Using a DVOM, measure resistance of PTO circuit between PCM harness connector terminal No. 4 and negative battery terminal. If resistance is 10 k/ohms or less, repair short to ground in PTO circuit. If resistance is more than 10 k/ohms, go to step  7).
   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 Circuit From PTO Switch Connector To PCM
   
   Reconnect PCM harness connector. Connect scan tool to DLC. Connect a jumper wire between positive battery terminal and PTO switch harness connector PTO terminal. See Fig 1. Turn ignition switch to ON position. Using scan tool, select PTO PID from PID/DATA MONITOR & RECORD. PTO PID value should be ON with jumper wire connected and OFF with jumper wire disconnected. If PTO PID value is not as specified, go to next step. If PTO PID value is as specified, PTO circuit from PTO switch to PCM is okay. Diagnose by symptom and repair as necessary. Go to SYMPTOMS in TROUBLE SHOOTING - NO CODES - EEC-V - CNG & GASOLINE article.
7. 8) Check PTO Circuit Resistance
   
   Turn ignition switch to OFF position. Disconnect PCM connector. Using a DVOM, measure resistance of PTO circuit between PCM harness connector terminal No. 4 and PTO switch harness connector PTO terminal. See Fig 1. 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. See DIAGNOSTIC TROUBLE CODE DEFINITIONS table. If no DTCs are present, go to next step.
NOTE: This test step will determine if applying an extra load on engine, such as operating the PTO, caused a Continuous Memory DTC to be stored.
9. 10) Perform OBD-II Drive Cycle With PTO Disengaged
   Ensure PTO is disengaged. Perform PCM RESET PROCEDURE under CLEARING CODES under SELF-DIAGNOSTIC SYSTEM. Perform DRIVE CYCLE PROCEDURES under ADDITIONAL SYSTEM FUNCTIONS. Ensure OBD-II DRIVE CYCLE PROCEDURES are performed to verify repair. Retrieve Continuous Memory DTCs. If any DTCs are present, service DTCs as necessary. See DIAGNOSTIC TROUBLE CODE DEFINITIONS table. If no DTCs are present, fault cannot be duplicated at this time. MIL illumination may have been caused by engaging PTO (creating an engine load), while OBD-II monitors were running. If symptom is still present, go to TEST Z, step 1) .