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Test QA: Unable To Activate Self-Test/Communication Error

NOTE: Perform this test when instructed during QUICK TEST or if directed by other test procedures. Repeat QUICK TEST after repairs are completed.
NOTE: See TEST DIRECTORY  table for starting diagnostic step.
CIRCUIT TERMINAL IDENTIFICATION (PCM)

Circuit PCM Terminal No. Wire Color
COMM 7 Green/Black
COMM 22 Gray/Red
COMM 24 Green/White
COMM 25 White
COMM 31 Pink/Black
COMM 33 Red/Green
DLC 17 Black/White
DLC 74 Yellow/Red
DLC 75 Yellow/Black
EVAP Canister Vent/DLC 88 Light Green/Black
GND 10 Black
GND 19 Black
GND 39 Black/Red
GND 45 Black/Red
GND 96 Black
GND 104 Black
KAPWR 80 Yellow
K-LINE 68 Yellow/Green
VPWR 20 Blue/Black
VPWR 38 Black/Yellow
VPWR 71 Blue/Yellow
CIRCUIT TERMINAL IDENTIFICATION (TCM)

Circuit TCM Terminal No. Wire Color
COMM 5A Green/White
COMM 6A White
COMM 7A Pink/Black
COMM 14A Gray/Red
COMM 15A Green/Black
COMM 17B Red/Green
DLC 6B Yellow/Red
DLC 7B Yellow/Black
GND 1B Black/Red
GND 24B Black/Red
KAPWR 4B Purple
VPWR 10A Light Green
VPWR 19A Light Green
TEST DIRECTORY

Fault Action
OBD-II Communication Error (1) Go To Step 1) 
No PCM Data Through Diagnostic Connector Go To Step 10) 
No TCM Data Through Diagnostic Connector Go To Step 20) 
DTC P0600 Or P1605 Go To Step 30) 
No DTCs Retrieved Manually (2) Go To Step 40) 
(1) Diagnostic data link functional on scan tool.
(2) No DTCs retrieved using diagnostic harness connector.

  1. 1) Verify Retrieval Procedure

    Turn ignition off. Inspect DLC and 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 TP sensor harness connector. Turn ignition on. Measure voltage between Brown wire (VREF) and Black/Yellow wire (SIG RTN) at TP sensor harness connector. If voltage is 4.5-5.5 volts, VREF is okay, go to next step. If voltage is not 4.5-5.5 volts, see TEST C: REFERENCE VOLTAGE under SYSTEM TESTS in appropriate SELF-DIAGNOSTICS article in ENGINE PERFORMANCE.

  3. 3) Check Ground At OBD-II DLC

    Turn ignition off. Inspect OBD-II DLC for damage. See CIRCUIT TERMINAL IDENTIFICATION (PCM)  table. See Fig 1 . Measure resistance between terminal 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 not less than 5 ohms, repair open ground circuit.

  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 not greater than 10 volts, repair open B+ circuit.

  5. 5) Check Ground At OBD-II DLC

    Turn ignition off. Measure resistance between terminal No. 5 (PWR GND) at OBD-II DLC and ground. If resistance is less than 5 ohms, go to next step. If resistance is not less than 5 ohms, repair open PWR GND circuit.

  6. 6) Check ISO Circuit Continuity

    Turn ignition off. Disconnect PCM. Measure resistance between terminal 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 not less than 5 ohms, repair open ISO circuit (Yellow/Green wire).

  7. 7) Check ISO Circuit For Short To Ground

    Disconnect PCM. Measure resistance between terminal 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 shorted ISO circuit (Green/Yellow wire).

  8. 8) Check ISO Circuit For Short To Power

    Disconnect PCM. Measure resistance between ISO circuit at PCM harness connector terminal No. 68 (Yellow/Green wire), VPWR, and KAPWR circuits at PCM. See CIRCUIT TERMINAL IDENTIFICATION (PCM)  table. See Fig 1 . If resistance is greater than 10 k/ohms, replace PCM. If resistance is not greater than 10 k/ohms, repair short to voltage in ISO 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 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 terminal No. 7 at DLC. If voltage is greater than 10 volts, go to next step. If voltage is not greater than 10 volts, repair Blue wire between interior fuse panel and diagnostic connector.

  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. Verify circuits do not have continuity (more than 10 k/ohms) to ground. If resistance measurements indicate open or shorted circuit, repair circuit in question. If resistance measurements are as specified, replace PCM.
    DATA TEST NO. 1

    PCM Connector Terminal No. DLC Terminal No.
    74 1
    75 2
    17 6
    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 terminal No. 7 at DLC. If voltage is greater than 10 volts, go to next step. If voltage is not greater than 10 volts, 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 terminals and DLC terminals. See DATA TEST NO. 2  table. Verify circuits do not have continuity (more than 10 k/ohms) to ground. If resistance measurements indicate open or shorted circuit, repair circuit in question. If resistance measurements are as specified, go to next step.
    DATA TEST NO. 2

    TCM Terminal No. DLC Terminal No.
    6B 13
    7B 12

  14. 22) Check Power & Ground To TCM

    Disconnect TCM. Measure voltage between VPWR and KAPWR and GND circuits at TCM harness connector. See CIRCUIT TERMINAL IDENTIFICATION (TCM)  table. See Figure . If at least 10 volts exist at all connector pin power/ground combinations, replace TCM. If any circuits are open, go to TEST B: TRANSMISSION FLUID TEMPERATURE SENSOR  .
    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. Measure resistance between COMM circuits and GND circuits at PCM and TCM connectors. See CIRCUIT TERMINAL IDENTIFICATION (PCM)  and CIRCUIT TERMINAL IDENTIFICATION (TCM)  tables. See Figure and Fig 1 . 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.
    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 not greater than 10 volts, check METER fuse (10-amp) located 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 harness connector and DLC (Blue/White wire). If resistance is greater than 5 ohms, repair Blue/White wire. If resistance is not greater than 5 ohms, go to TEST B: TRANSMISSION FLUID TEMPERATURE SENSOR  to verify PCM power supply. If results of TEST B are positive (power to PCM okay), replace PCM.
Fig 1: Identifying OBD-II DLC Terminals & PCM Terminals
G99F02332Courtesy of FORD MOTOR CO.
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