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:

• ISO communication harness circuit.
• GND and B+ harness circuit.
• Faulty PCM.
• Faulty Transmission Control Module (TCM).

1. 1) Verify Retrieval Procedure
   
   Turn ignition off. Inspect DLC and New Generation Star (NGS) tester connector terminals. Repair as necessary. Ensure correct procedures were used to retrieve DTCs. See QUICK TEST . If no fault can be found in DTC 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 VREF and SIG RTN circuits at TP sensor harness connector. See Figure. If voltage reading 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. 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 DLC Circuits & Terminals

   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). See Fig 1. If voltage is greater than 10 volts, go to next step. If voltage is not greater than 10 volts, repair open B+ circuit.
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.
6. 6) Check ISO Circuit Continuity
   
   Disconnect PCM harness connector. Check resistance between pin No. 7 at OBD-II DLC and ISO circuit (Yellow/Green wire) at PCM harness connector terminal No. 68. See Figure and Fig 1 . If resistance is less than 5 ohms, go to next step. If resistance is not less than 5 ohms, repair open in circuit.
7. 7) Check ISO Circuit For Short To Ground
   
   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 not greater than 10 k/ohms, repair short in circuit.
8. 8) Check ISO Circuit For Short To Power
   
   Measure resistance between ISO and KAPWR circuits at PCM harness connector. See CIRCUIT PIN IDENTIFICATION (PCM)  table. If resistance is greater than 10 k/ohms, replace PCM. If resistance is not greater than 10 k/ohms, repair short to voltage in circuit.
   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 function of NGS tester. If tester communicates properly with PCM, go to next step. If tester does not communicate properly with PCM, go to step  1).
10. 11) Check Ignition Switch Input To DLC
    
    Turn ignition on. Measure voltage between ground and pin No. 8 at DLC. See Fig 1. If voltage is greater than 10 volts, go to next step. If voltage is not greater than 10 volts, repair open in circuit.
11. 12) Check Circuits Between PCM & DLC
    
    Turn ignition off. Disconnect PCM harness connector. Inspect connector for damage. Measure resistance between appropriate PCM harness connector terminals and DLC terminals. See DATA TEST NO. 1  table. See Figure and Fig 1 . Also, measure resistance between ground appropriate PCM pins.

    Resistance between the DLC and PCM pins should be less than 5 ohms. Resistance between ground and PCM pins should be greater than 10 k/ohms. If resistance readings are as specified, replace PCM. If resistance readings are not as specified, repair affected circuit(s).

    DATA TEST NO. 1
    
    

    PCM Connector Terminal No.	DLC Terminal No.
    74	13
    75	12
    17	1

    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 Ignition Switch Input To DLC
    
    Turn ignition on. Measure voltage between ground and pin No. 8 at DLC. See Fig 1. If voltage is greater than 10 volts, go to next step. If voltage is not greater than 10 volts, repair open in circuit.
13. 21) Check Circuits Between TCM & DLC
    
    Turn ignition off. Disconnect TCM harness connector. Inspect connector for damage. Measure resistance between appropriate DLC and TCM harness connector pins. See DATA TEST NO. 2  table. Also, measure resistance between ground appropriate TCM pins.

    Resistance should be less than 5 ohms between TCM and DLC pins. Resistance should be greater than 10 k/ohms between TCM pins and ground. If resistance measurements are as specified, go to next step. If resistance measurements are not as specified, repair affected circuit(s).

    DATA TEST NO. 2
    
    

    TCM Pin No.	DLC Pin No.
    6	13
    7	12

14. 22) Check Power & Ground To TCM
    
    Turn ignition on. Measure voltage between VPWR and KAPWR and GND circuits at TCM harness connector. See CIRCUIT PIN IDENTIFICATION (TCM)  table. If voltage reading between all power and ground circuits are greater than 10 volts, replace TCM. If voltage reading between all power and ground circuits are not greater than 10 volts, 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 harness connectors. Measure resistance between TCM and PCM COMM circuits. 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). 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. Reconnect 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. Measure voltage on DLC terminal No. 8. See Fig 1. If voltage is greater than 10 volts, go to next step. If voltage is not greater than 10 volts, check 10-amp METER fuse in interior fuse panel. Replace as necessary. If fuse is okay, repair open in circuit between interior fuse panel and DLC. See WIRING DIAGRAMS article.
17. 41) Check Continuity Of Blue/White Wire
    
    Turn Ignition off. Disconnect PCM and DLC harness connectors. Check continuity of DLC input circuit (Blue/White wire) between PCM harness connector and DLC. See WIRING DIAGRAMS article. If resistance is greater than 5 ohms, repair open in circuit. If resistance is not greater than 5 ohms, go to TEST B .