U0102: Lost Communication With Transfer Case Control Module
What to do
Expect the four-wheel-drive selector to stop responding — the vehicle keeps whichever mode it was in and will not change.
Check which mode that is, because it matters. Left in two-wheel drive it is simply an inconvenience. Left in a locked four-wheel-drive or low-range setting, avoid dry tarmac and tight turns — the axles fight one another when the surface will not let a wheel slip, which causes binding, scrubbed tyres and driveline wear. If the car judders or feels like it is dragging in tight turns, that is what is happening.
This module sits underneath the vehicle where its connector takes water, salt and stones, so ask for that and the wiring to be inspected before the module is condemned.
What this code means
The transfer case control module has stopped being heard from. The general reasoning is at U0100.
A transfer case splits drive between front and rear axles on a four-wheel-drive vehicle, and its module is what selects high range, low range and any locking or on-demand behaviour. Losing communication with it means the current state is held rather than changed — so the vehicle keeps whatever mode it was in and refuses to switch, which is the safe response given that shifting a transfer case at the wrong moment is mechanically destructive.
The practical consequence depends entirely on which mode it was left in, and that is worth checking before anything else. Stuck in two-wheel drive is an inconvenience. Stuck in a locked four-wheel-drive or low-range mode is not — a locked centre differential on a dry road makes the axles fight each other through corners, which produces binding, tyre scrub and driveline wear.
This module lives under the vehicle, so its connector takes road salt, water and stone chips, and that is where these faults usually are.
Likely causes
Start here
- Corroded or loose connector · easy
- Damaged data bus wiring · moderate
- Water ingress into connector · moderate
Less common
- Failed power or earth supply to the module · moderate
- Faulty transfer case control module · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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