Powertrain, generic (extended)

P2686 Actuator Supply Voltage C Circuit High

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modePossible

The high case of supply C concerns voltage that should not be there: the rail stays live although the controller has turned it off. Causes are an internal high-side switch that no longer opens or an outside wire touching battery positive. GM's 2023 and 2024 TCM tables run this check during shutdown. With output 7 disabled, a reading above 70 % of battery voltage counts as a shorted switch; the module keeps that finding in permanent memory and reports it once restarted. Battery voltage must stay within 1.5 V during the test, and GM files it as Type B: two failing trips before the lamp lights. Ford lists P2686 as the shorted-switch fault of high side driver 7 in its 2024 TR9070 table and also in the Boss 302S code list. The solenoids can no longer be switched off safely, so a limp mode is likely.

Likely causes

Internal high-side switch of the controller stuck conducting

Supply wire shorted to a battery-fed circuit in the harness

Moisture in the transmission connector creating a leakage path

Symptoms

MIL after a second trip with the fault
Limp mode or fixed gear after restart
Code returns after clearing once the key has been off

Repair estimate

DifficultyHardWorkshop job

Parts and labour€150–1,800

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 P2685 P2671 P0659 P26E9 P0883

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