Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Pinpoint Test I: U0166:87
- Refer to Wiring Diagrams Module Communications Network
for schematic and connector information.
Normal Operation and Fault Conditions
REFER to: Communications Network - Overview .
DTC Fault Trigger Conditions
DTC Description Fault Trigger Condition BCM U0166:87 Lost Communication With Auxiliary Heater Control Module: Missing Message A continuous memory DTC that sets in the BCM if messages from the AHCM through the GWM are missing. Possible Sources
- Communication network concern
- Battery voltage concern
- GWM concern
- AHCM
- BCM
- NOTE: If new modules were installed prior to the DTC being set, the module configuration may be incorrectly set during the PMI or the PMI may not have been carried out.
- I1 CHECK THE COMMUNICATION NETWORK
- Ignition ON.
- Connect the diagnostic tool.
- Using a diagnostic scan tool, perform a network test.
Does the AHCM pass the network test?
Yes GO to I2 No REFER to: Communications Network . - I2 CHECK THE BCM (BODY CONTROL MODULE) CONTINUOUS MEMORY DIAGNOSTIC TROUBLE CODES (CMDTCS)
- Using a diagnostic scan tool, clear the Diagnostic Trouble Codes (DTCs).
- Wait 10 seconds.
- Using a diagnostic scan tool, check the BCM CMDTCs.
Is DTC B11D9:16, B11D9:17, U3006:16, U3006:17, U3007:16, U3007:17, U3013:16, U3013:17, U3014:16 or U3014:17 recorded?
Yes For DTC B11D9:16, U3006:16, U3007:16, U3013:16 or U3014:16, GO to Pinpoint Test W For DTC B11D9:17, U3006:17, U3007:17, U3013:17 or U3014:17, GO to Pinpoint Test X No GO to I3 - I3 RETRIEVE THE AHCM (AUXILIARY HEATER CONTROL MODULE) DTCS
- Using a diagnostic scan tool, perform the AHCM self-test.
Are any voltage system related DTCs present?
Yes REFER to: Climate Control System . No GO to I4 - I4 RECHECK THE BCM (BODY CONTROL MODULE) CMDTCS
- Using a diagnostic scan tool, clear the DTCs.
- Wait 10 seconds.
- Using a diagnostic scan tool, check the BCM CMDTCs.
Is DTC U0166:87 still present?
Yes GO to I5 No The system is operating correctly at this time. The DTC may have been set due to high network traffic or an intermittent fault condition. - I5 CHECK FOR DTC (DIAGNOSTIC TROUBLE CODE) U0166:87 SET IN OTHER MODULES
- Using a diagnostic scan tool, clear the Diagnostic Trouble Codes (DTCs).
- Ignition OFF.
- Wait 10 seconds.
- Ignition ON.
- Using a diagnostic scan tool, retrieve all CMDTCs.
Is DTC U0166:87 set in other modules?
Yes GO to I6 No GO to I7 - I6 CHECK FOR CORRECT AHCM (AUXILIARY HEATER CONTROL MODULE) OPERATION
- Ignition OFF.
- Disconnect and inspect the AHCM connector.
- Repair:
- corrosion (install new connector or terminals - clean module pins)
- damaged or bent pins - install new terminals/pins
- pushed-out pins - install new pins as necessary
- Reconnect the AHCM connector. Make sure it seats and latches correctly.
- Operate the system and determine if the concern is still present.
Is the concern still present?
Yes CHECK OASIS for any applicable service articles: TSB, GSB, SSM or FSA. If a service article exists for this concern, DISCONTINUE this test and FOLLOW the service article instructions. If no service articles address this concern, INSTALL a new AHCM. REFER to Heating, Ventilation And Air Conditioning (HVAC) Control Module . No The system is operating correctly at this time. The concern may have been caused by module connections. ADDRESS the root cause of any connector or pin issues. - I7 CHECK FOR CORRECT BCM (BODY CONTROL MODULE) OPERATION
- Ignition OFF.
- Disconnect and inspect the BCM connectors.
- Repair:
- corrosion (install new connector or terminals - clean module pins)
- damaged or bent pins - install new terminals/pins
- pushed-out pins - install new pins as necessary
- Reconnect the BCM connectors. Make sure they seat and latch correctly.
- Operate the system and determine if the concern is still present.
Is the concern still present?
Yes CHECK OASIS for any applicable service articles: TSB, GSB, SSM or FSA. If a service article exists for this concern, DISCONTINUE this test and FOLLOW the service article instructions. If no service articles address this concern, INSTALL a new BCM. REFER to: Body Control Module (BCM) . No The system is operating correctly at this time. The concern may have been caused by module connections. ADDRESS the root cause of any connector or pin issues.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.