Possible Causes

• Network communication concern
• Battery or charging system concerns
• Stoplamp switch
• PCM
• ABS module

Harness Side

1. I1: CHECK THE COMMUNICATION NETWORK 
   • Ignition ON, engine OFF.
   • Press the Read Vehicle Information button to view the results of the modules communicating on the network.
   • Retrieve the continuous memory DTCs.
   • Does the PCM pass the Network Test? 

     Yes	No
     Go to  I2.	DIAGNOSE the PCM does not communicate with the diagnostic scan tool. Refer to Module Communications Network article.

2. I2: RECHECK FOR DTC P1571:64 
   • Carry out the ABS self-test.
   • Clear the ABS DTCs.
   • Ignition OFF.
   • Ignition ON, engine OFF.
   • Carry out the ABS self-test.
   • Record all retrieved ABS module DTCs.
   • Is DTC P1571:64 retrieved again? 

     Yes	No
     Go to  I3.	If no DTCs are present, the system is operating correctly at this time. The DTC may have been set due to high network traffic or an intermittent fault condition. If DTC U0100:xx, U0101:xx, U0104:xx, U0401:xx, U0402:xx or U0405:xx is present, Go to  I5.

3. I3: INSPECT THE STOPLAMP SWITCH 
   • Inspect the stoplamp switch for correct installation and obvious signs of damage.
   • Observe the stoplamp switch while pressing and releasing the brake pedal.
   • Is the stoplamp switch correctly installed, free from obvious signs of damage and does it operate correctly? 

     Yes	No
     Go to  I5.	If the switch is damaged, INSTALL a new stoplamp switch. Refer to Exterior Lighting article If the switch is not installed correctly or does not operate correctly, Go to  I4.

4. I4: VERIFY BRAKE PEDAL SWITCH INSTALLATION 
   NOTE: Follow all notes and cautions in the stoplamp switch removal and installation procedure.
   • Remove and install the stoplamp switch. Refer to the Exterior Lighting article.
   • Test drive the vehicle at speeds above 20 km/h (12 mph) and carry out at least 2 complete stops.
   • Carry out the ABS self-test.
   • Is DTC P1571:64 retrieved again? 

     Yes	No
     Go to  I5.	The system is operating correctly at this time. The DTC may have been set due to an incorrectly installed stoplamp switch.

5. I5: REVIEW THE ABS MODULE SELF-TEST FOR VOLTAGE-RELATED DTCS 
   • Review the recorded DTCs from the ABS self-test.
   • Is DTC U3003:16 or U3003:17 present? 

     Yes	No
     For DTC U3003:16, Go to PINPOINT TEST A . For DTC U3003:17, Go to PINPOINT TEST F .	Go to  I6.

6. I6: CHECK FOR PCM DTCS 
   • Carry out the PCM KOEO self-test.
   • Are any DTCs present? 

     Yes	No
     DIAGNOSE the PCM DTC. REFER to applicable Electronic Engine Controls article	Go to  I7.

7. I7: CHECK FOR OTHER CAUSES OF COMMUNICATION NETWORK CONCERN 
   NOTE: If new modules were installed prior to the DTC being set, the module configuration can be incorrectly set during the PMI or the PMI may not have been carried out.
   • Check the vehicle service history for recent service actions related to the PCM or the ABS module. If recent service history is found:
     • Verify the correct replacement module was installed. HVBOM may be used to verify correct part fitment.
     • Verify the configuration of replacement module was correct. Re-configure the module using as-built data if prior configuration is suspect.
     • Verify the module was not obtained from a like vehicle and installed into customer vehicle. Return the swapped module to source vehicle and obtain new replacement module.
   • Operate the system and determine if the observable symptom is still present.
   • Is the observable symptom still present? 

     Yes	No
     Go to  I8.	The system is operating correctly at this time. The concern may have been due to incorrect parts replacement procedures or incorrect module configuration.

8. I8: CHECK FOR LOST COMMUNICATION DTC SET IN OTHER MODULES 
   • Retrieve the continuous memory DTCs.
   • Is DTC P1571:64, U0100:xx, U0101:xx, U0104:xx, U0401:xx, U0402 or U0405:xx set in 1 or more modules in addition to the ABS module? 

     Yes	No
     Go to  I9.	Go to  I10.

9. I9: VERIFY PCM OPERATION 
   • Ignition OFF.
10. I10: VERIFY ABS MODULE OPERATION 
    • Ignition OFF.
    • ABS Module connector disconnected. (C135)