Diagnostic Aids

Perform this test when instructed during QUICK TEST  or if directed by other test procedures. This test is used to diagnose the following:

• Communication harness circuit: ISO.
• Harness circuits: GND and B+.
• Faulty PCM.
• Faulty TCM.

1. 1) Verify Retrieval Procedure
   
   Turn ignition off. Inspect DLC and scan tool connector terminals. Repair as necessary. Verify that the correct procedures were used to retrieve trouble codes. See QUICK TEST . If no fault can be found in code retrieval procedure and data cables are okay, go to next step.
2. 2) Check For VREF At TP Sensor
   
   Turn ignition off. Disconnect Throttle Position (TP) sensor harness connector. Turn ignition on. Measure voltage between Brown wire (VREF) and Black/Yellow wire (SIG RTN). If voltage is 4.5-5.5 volts, VREF is okay, go to next step. If voltage is not 4.5-5.5 volts, go to TEST C .
3. 3) Check Ground At OBD-II DLC
   
   Turn ignition off. Inspect OBD-II DLC for damage. See Fig 1. Also see CIRCUIT PIN IDENTIFICATION (PCM)  table. Measure resistance between pin No. 4 (ground) at OBD-II DLC and chassis ground on engine block. If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, repair open ground circuit. Repeat QUICK TEST .
   Fig 1: Identifying OBD-II Data Link Connector Terminals & Test Pins

   Courtesy of FORD MOTOR CO.
4. 4) Check Power At OBD-II DLC
   
   Turn ignition on. Measure voltage between OBD-II terminals No. 16 (B+) and No. 4 (GND). If voltage is greater than 10 volts, go to next step. If voltage is less than 10 volts, repair open B+ circuit. Repeat QUICK TEST .
5. 5) Check Ground At OBD-II DLC
   
   Turn ignition off. Measure resistance between pin No. 5 (PWR GND) at OBD-II DLC and ground. If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, repair open PWR GND circuit. Repeat QUICK TEST .
6. 6) Check ISO Circuit Continuity
   
   Turn ignition off. Disconnect PCM. Measure resistance between pin No. 7 at OBD-II DLC and ISO circuit terminal No. 68 (Yellow/Green wire). If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, repair open ISO circuit (Yellow/Green wire). Repeat QUICK TEST .
7. 7) Check ISO Circuit For Short To Ground
   
   Disconnect PCM. Measure resistance between pin No. 7 at OBD-II DLC and ground. If resistance is greater than 10 k/ohms, go to next step. If resistance is less than 10 k/ohms, repair shorted ISO circuit (Green/Yellow wire). Repeat QUICK TEST .
8. 8) Check ISO Circuit For Short To Power
   
   Disconnect PCM. Measure resistance between ISO circuit at PCM connector terminal No. 68 (Yellow/Green wire), VPWR (Black/White) terminal No. 71, and KAPWR (Yellow wire) terminal No. 80. If resistance is greater than 10 k/ohms, replace PCM. Repeat QUICK TEST . If resistance is less than 10 k/ohms, repair short to voltage in ISO circuit. Repeat QUICK TEST.
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 8) to step 10). No test procedures have been omitted.
9. 10) Check OBD-II Communication
   
   Retrieve DTCs using generic OBD-II function of scan tool. If scan tool communicates properly with PCM, go to next step. If scan tool does not communicate properly with PCM, go to step  1.
10. 11) Check Power To Diagnostic Connector
    
    Turn ignition on. Measure voltage between ground and pin No. 7 at DLC. See Fig 2. Also see CIRCUIT PIN IDENTIFICATION (TCM)  table. If voltage is greater than 10 volts, go to next step. If less than 10 volts are present, repair Blue wire between interior fuse panel and diagnostic connector.
    Fig 2: Identifying Fuse Panel Diagnostic Connector Terminals & Test Pins

    Courtesy of FORD MOTOR CO.
11. 12) Check Circuits Between PCM & DLC
    
    Turn ignition off. Disconnect PCM and inspect connector for damage. Measure resistance between PCM connector terminals and DLC terminals. Verify continuity (less than 5 ohms) between PCM and DLC terminals. See DATA TEST NO. 1  table. Also verify circuits do not have continuity (greater than 10 k/ohms) to ground.
    DATA TEST NO. 1
    
    

    PCM Connector Terminal No.	DLC Terminal No.
    74	1
    75	2
    17	6

    If resistance measurements indicate open or shorted circuit, repair circuit in question. If resistance measurements are as specified, replace PCM. Restore all electrical connections and repeat QUICK TEST .

    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 12) to step 20). No test procedures have been omitted.
12. 20) Check Power To DLC
    
    Turn ignition on. Measure voltage between ground and pin No. 7 at DLC. If more than 10 volts are present, go to next step. If 10 volts or less are present, repair Blue wire between interior fuse panel and diagnostic connector.
13. 21) Check Circuits Between TCM & DLC
    
    Turn ignition off. Disconnect TCM and inspect connector for damage. Verify continuity (less than 5 ohms) between TCM pins and DLC pins. See DATA TEST NO. 2  table. Also verify circuits do not have continuity (greater than 10 k/ohms) to ground.
    DATA TEST NO. 2
    
    

    TCM Pin No.	DLC Pin No.
    6B	1
    7B	2

    If resistance measurements indicate open or shorted circuit, repair circuit in question. If resistance measurements are as specified, go to next step. Restore all electrical connections and repeat QUICK TEST .

14. 22) Check Power & Ground To TCM
    
    Disconnect TCM. Measure voltage between VPWR and KAPWR and GND circuits at TCM harness connector. See CIRCUIT PIN IDENTIFICATION (TCM)  table. If at least 10 volts exist at all connector pin power/ground combinations, replace TCM. If any circuits are open, go to TEST B .
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 22) to step 30). No test procedures have been omitted.
15. 30) Check Data Circuits Between PCM & TCM
    
    Turn ignition off. Disconnect PCM and TCM. Measure resistance between TCM and PCM COMM circuits. Also measure resistance between COMM circuits and GND at PCM and TCM connectors. See CIRCUIT PIN IDENTIFICATION (PCM)  and CIRCUIT PIN IDENTIFICATION (TCM)  tables. Verify circuits have continuity (less than 5 ohms). Also verify circuits do not have continuity to ground (less than 10 k/ohms). If resistance measurements indicate open or shorted circuit, repair circuit in question. If resistance measurements are as specified, replace TCM. If symptoms still exist, replace PCM. Restore all electrical connections and repeat QUICK TEST 
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 30) to step 40). No test procedures have been omitted.
16. 40) Check Power At DLC
    
    Turn ignition on. Disconnect DLC for malfunction indicator light (MIL). Turn ignition on. Measure voltage on Blue wire at diagnostic connector. If voltage is greater than 10 volts, go to next step. If voltage is 10 volts or less, check 10-amp METER fuse in interior fuse panel. Replace fuse if necessary. If fuse is okay, repair open Blue wire between interior fuse panel and diagnostic connector.
17. 41) Check Continuity Of Blue/White Wire
    
    Turn Ignition off. Disconnect PCM and diagnostic connector. Check continuity of DLC input circuit between PCM connector and DLC (Blue/White wire). If resistance is greater than 5 ohms, repair Blue/White wire circuit. If resistance is less than 5 ohms, go to TEST B  to verify PCM power supply. If results of TEST B are positive (power to PCM okay), replace PCM.