Gear Shift Module Communication Circuit Low
The P0861 code means the vehicle's onboard diagnostic system has detected: Gear Shift Module Communication Circuit Low. This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- hard
- Estimated cost
- $200 - $1,000 (parts and labor)
Read and clear transmission codes. Many trans codes are caused by low or burnt fluid -- check level and color before assuming the worst.
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Common Symptoms
- Check Engine Light illuminated
- Shift module communication lost
- Transmission stuck in current gear or Park
- Gear indicator not responding
Probable Causes (Ranked by Likelihood)
- CAN bus low wire shorted to ground Very High
- Gear shift module internal failure pulling bus low High
- Damaged CAN bus wiring harness Moderate
- Water intrusion in gear shift module connector Low
Step-by-Step Diagnostic Procedure
-
Measure CAN bus voltage levels at the shift module connector
-
Disconnect shift module and check if CAN bus recovers on other modules
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Inspect CAN bus wiring for damage, especially near the center console
-
Check for water intrusion at the shift module
Frequently Asked Questions
What does circuit low mean on a CAN bus?
CAN bus communication uses two wires (CAN high and CAN low). A circuit low fault means the CAN low wire is shorted to ground or the shift module is pulling the bus voltage below normal operating range.
Can a shorted shift module affect other systems?
Yes, a module that shorts the CAN bus can disrupt communication with all other modules on the same bus, causing multiple system faults.
Is the gear shift module repairable?
In most cases the module must be replaced and reprogrammed. Some specialty shops can repair electronic modules, but replacement is more common.
Sources
This page is built from documented references. Verify against your own service info before repair work.
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