Test FB: Power Take Off: Testing

NOTE: Diagnostic procedures beginning with step 1) are performed when directed here from TEST QA, step 20) , or TEST QC, step 2) .

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 PWR In Aftermarket Switch Or VPWR
- Faulty Powertrain Control Module (PCM)
Turn ignition switch to OFF position. Disconnect PTO switch connector. Using a DVOM, measure resistance between PTO switch terminals. See Figure. With PTO switch in OFF position, resistance should be more than 10 k/ohms. With PTO switch in ON position, 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. Refer to aftermarket component manufacturer for service information. Reconnect PTO switch connector. Perform DRIVE CYCLES . Ensure OBD-II DRIVE CYCLE is performed to verify repair.

2) Check PTO Circuit For Short To VPWR

Ensure ignition switch is in OFF position. 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 PTO circuit at PCM harness connector 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 PTO circuit for short to VPWR.

NOTE: Diagnostic procedures beginning with step 3) are performed when directed here from SYMPTOMS in TROUBLE SHOOTING - NO CODES - CNG, FLEX-FUEL & GASOLINE article.

3) MIL On: Check PTO PID
Possible causes are:
- PTO Circuit Open
- PTO Circuit Shorted To Chassis Ground
Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC). Turn ignition switch to ON position. Using scan tool, access 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 available, go to step 9).

NOTE: This test step requires operating PTO. Refer to PTO manufacturer operating manual for operating instructions and safety precautions.

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 - CNG, FLEX-FUEL & GASOLINE article. If PTO PID value does not cycle as specified, go to next step.

5) Check PTO Circuit For Short To Ground In Harness

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 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.

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 (B+) and PTO circuit at PTO switch harness connector. See Figure. Turn ignition switch to ON position. Using scan tool, access PTO PID from PID/DATA MONITOR & RECORD. If PTO PID value is ON with jumper wire connected and OFF with jumper wire disconnected, PTO circuit is okay. Diagnose by symptom and repair as necessary. Go to SYMPTOMS in TROUBLE SHOOTING - NO CODES - CNG, FLEX-FUEL & GASOLINE article. If PTO PID value is not as specified, go to next step.

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 and PTO switch harness connector. See Figure. If resistance is less than 5 ohms, replace PCM. If resistance is 5 ohms or more, repair open in PTO circuit.

NOTE: This test step is for diagnosing PTO when vehicle does not support PTO circuit or PTO PID.

9) Perform KOEO & KOER Self-Tests
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 . 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 PTO, caused a Continuous Memory DTC to be stored.

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 CYCLES . Ensure OBD-II DRIVE CYCLE is performed to verify repair. Retrieve Continuous Memory DTCs. If any DTCs are present, service DTCs as necessary. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . 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) .