Powertrain, generic (extended)

P2C46 Battery Isolation/Voltage Stabilization Control Circuit High

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

P2C46 is the opposite of P2C45: the control line of the battery isolation or voltage stabilization switch sits higher than expected, which points to a short to battery voltage, or, on a low-side driven relay, to an open circuit that leaves the sense input floating high. The consequence can be worse than with a low signal, because a switch that cannot be commanded may stay closed during restarts, so the supply dip the stage is meant to block reaches the electronics again; Ford's start-stop patent describes the main battery sagging to roughly 5–7 V while cranking. No manufacturer documents P2C46 openly, so the exact threshold is calibration-specific. Check for wires pinched against B+ cables, then for an open circuit, before replacing the isolator.

Likely causes

Control wire shorted to battery positive
Open circuit with low-side driver (input pulled high)
Isolator internally defective
Control module input or driver fault

Symptoms

  • Fault indicator on
  • Stop-start disabled
  • Screens or radio may reset when the engine restarts

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–500
Time0.5–2.5 h

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

Parts involved

battery isolation modulewiring harnessecm

Related codes

P2C43P2C44P2C45P2C47U061E

References: patents.google.com, law.cornell.edu, en.wikipedia.org.