Diagnostic Aids

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

Fig 1: Identifying PTO Circuit & Switch Schematic

Courtesy of FORD MOTOR CO.

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. 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 (GASOLINE) article.

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) 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 (GASOLINE) article. If PTO PID value does not cycle as specified, go to next step.

5) Check PTO Circuit For Short To Ground

Turn ignition switch to OFF position. Disconnect PCM connector(s). Disconnect PTO switch connector. Disconnect scan tool from Data Link Connector (DLC). Measure resistance between PCM connector terminal No. 4 and negative battery terminal. If resistance is 10 k/ohms or less, repair short circuit. If resistance is more than 10 k/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.

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 harness connector. Turn ignition switch to ON position. 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.

8) Check Circuit Resistance

Turn ignition switch to OFF position. Disconnect PCM connector(s). Measure resistance between PCM connector terminal No. 4 and PTO terminal at PTO switch harness connector. If resistance is less than 5 ohms, replace PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Program PCM. See FLASH VEHICLE IDENTIFICATION BLOCK PROCEDURE . If resistance is 5 ohms or more, repair open in PTO circuit.

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.

10) Perform Drive Cycle

Ensure PTO is disengaged. Perform OBD-II DRIVE CYCLE. See DRIVE CYCLE PROCEDURES 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 .