TCM Communication Circuit Low
The P0865 code means the vehicle's onboard diagnostic system has detected: TCM Communication Circuit Low. This is a critical severity code.
- Keep driving?
- No — stop driving
- DIY difficulty
- hard
- Estimated cost
- $300 - $2,000 (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.
Basic scanners only read engine codes. This reads transmission, ABS, and airbag too.
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What Are the Symptoms of P0865?
- Check Engine Light illuminated
- Complete loss of TCM communication
- Transmission locked in one gear
- Unable to scan TCM with diagnostic tool
What Causes P0865? (Most Likely First)
- CAN bus low wire shorted to ground at or near TCM Very High
- TCM CAN bus transceiver failure High
- Damaged wiring harness near transmission Moderate
- TCM ground circuit problem Low
Can I Still Drive with P0865?
No — stop driving. P0865 is rated critical severity. Continuing to drive in this state risks further damage — get it looked at before your next trip.
Frequently Asked Questions
Why can the scan tool not connect to the TCM?
If the CAN bus low wire is shorted to ground, the TCM cannot transmit or receive data. The scan tool will show no communication with the TCM module.
Can a wiring repair fix P0865?
If the CAN bus wire is damaged, repairing or replacing the wire can restore communication. If the TCM internal transceiver is failed, the TCM must be replaced.
Should I have the vehicle towed?
Yes. With no TCM communication, the transmission is in an uncontrolled state and should not be driven. Have the vehicle towed to avoid further damage.
Mechanics Guide Step-by-step diagnosis
How Do You Diagnose P0865?
-
Measure CAN bus low voltage at the TCM connector (should be around 2.5V idle)
-
Disconnect TCM and check if CAN bus communication restores on other modules
-
Inspect wiring harness near the transmission for damage from heat or road debris
-
Check TCM ground connections
Sources 1
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
Which Vehicles Commonly Get P0865?
- 2007-2017 Dodge Ram 2500
- 2008-2018 Chrysler 200
- 2010-2020 Jeep Wrangler
- 2009-2019 Ford Explorer
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