P0859
PowertrainTransmissionmoderate severityTCM Communication Circuit Low
What P0859 Means
The TCM communication circuit voltage is lower than expected. This may prevent proper data transfer between control modules.
Symptoms
- Transmission fault indicator
- Loss of shift control
- Stored communication codes
Common Causes
- Short to ground in circuit
- Corroded connectors
- Faulty TCM
- Wiring harness damage
Diagnostic Steps
- Retrieve stored trouble codes
- Inspect circuit for short to ground
- Measure circuit voltage
- Verify TCM operation
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ANCEL AD410 →
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Serious DIY~$100
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Autel MaxiCOM MK808S →
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Autel MaxiSys MS906 Pro →
Full-system pro platform — topology mapping, ECU coding, the works.
✓ Autel official store
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