P0888: Transmission Control Module Power Relay Sense Circuit
What to do
If this is the only relay code stored, the supply is probably working and the module just cannot verify it. If a control circuit code is stored as well, the relay itself is more likely at fault.
What this code means
A fault in the circuit by which the module checks whether the relay actually did what it was told. Control and sense are deliberately separate: one commands the relay, the other confirms the result, and having both is what lets the module tell "I asked and it refused" from "I never asked".
That distinction is more useful than it sounds. A sense circuit fault on its own means the relay is probably working and the module simply cannot confirm it — a monitoring problem rather than a power problem. A sense fault alongside a control fault means the relay genuinely is not responding. Reading the two together saves replacing a relay that is fine.
Likely causes
Start here
- Open circuit in relay sense wiring · moderate
- Faulty transmission control module power relay · easy
- Corroded or loose connector · easy
Less common
- Poor module ground connection · moderate
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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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
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