Cause
Welded relay contacts
A relay whose contacts have fused closed, so the circuit it controls stays permanently powered. A relay switching an inductive load draws an arc every time it opens, and that arc erodes and eventually welds the contacts — so this is a wear-out failure of a component nobody treats as a wearing part.
The signature is a device that runs when it should not and cannot be switched off, including with the ignition off — a fuel pump that keeps running, a fan that will not stop, a heater that stays on. A component that runs continuously and flattens the battery overnight is a welded relay far more often than it is a module commanding it.
The module detects it by monitoring the circuit it thinks it switched off. Seeing voltage present when it commanded none, it reports a control circuit fault — naming the circuit rather than the relay. Swap the relay with an identical one elsewhere in the box as a first test, which is free and definitive. Ask what welded it: a shorted or stalling motor draws current well beyond the relay's rating, so the new relay welds too unless the load is checked.
Typically an easy fix. Often worth checking before paying anyone to look.
Codes this can cause (5)
Codes where this is a likely explanation first, rather than merely a possible one.
- P0889 Transmission Control Module Power Relay Sense Circuit Range/Performance Likely for this code High
- P0946 Hydraulic Pump Relay/Control Circuit Range/Performance Likely for this code High
- P0947 Hydraulic Pump Relay/Control Circuit Low Likely for this code High
- P2444 Secondary Air Injection System Pump Stuck On Bank 1 Likely for this code High
- P2446 Secondary Air Injection System Pump Stuck On Bank 2 Likely for this code High
Information, not instruction
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