Powertrain, generic (extended)

P2685 Actuator Supply Voltage C Circuit Low

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

P2685 means the third actuator supply rail sags while it is switched on, almost always because the line or one of the loads it feeds has a path to ground. Unlike the open and switch faults of this rail, GM's 2023 and 2024 TCM tables check this one continuously during operation: if the voltage at high-side output 7 falls below a share of the supply, or the averaged output current runs too high, a timer counts up and the fault is confirmed after 60 ms. Battery voltage must lie between 8.75 and 18 V, the engine must not be cranking, and the test is suspended when P0882 or P0883 is present; GM rates it Type A. Ford's 2024 summary lists P2685 as the shorted-load fault of high side driver 7 in the TR9070 dual-clutch unit. The protected output switches off and the transmission falls back to a failsafe mode.

Likely causes

Supply wire chafed through and touching ground

Shorted solenoid coil on this rail drawing excess current

Weak battery or charging fault pulling the whole supply down

Symptoms

MIL on during the same trip
Failsafe gear, no normal shifting
Blown fuse possible on the transmission supply

Repair estimate

DifficultyHardWorkshop job

Parts and labour€100–1,500

Time1–5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

actuator supply ccharging system

Related codes

P2684 P2686 P2670 P0658 P26E8 P0882

References: gsi.ext.gm.com, gsi.ext.gm.com, fordservicecontent.com.