Powertrain, generic (extended)

P2C43 Battery Isolation/Voltage Stabilization Control Circuit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

Some vehicles split their 12 V system with a switch so that a heavy starter load, typically an automatic restart, cannot pull the supply of control units and displays down. A Ford patent on start-stop cars puts that dip at roughly 5 to 7 V without such separation. The switch, a relay or semiconductor isolator, is commanded by a control module, and P2C43 is the general fault of this command line, usually an open circuit or a driver that sees no plausible load. No manufacturer documents P2C43 publicly; the only published case in this family is Ford's PowerBoost F-150 with an auxiliary battery isolator, which stores the performance code P2C44. Low, high and intermittent faults have their own codes P2C45 to P2C47. Expect auto stop-start or electric assist to be held back and a fault lamp; driving normally remains possible.

Likely causes

Open control wire or loose connector at the isolator
Isolator relay coil or electronic switch failed
Poor ground connection of the isolator circuit
Output driver in the control module defective

Symptoms

  • Warning lamp or powertrain fault indicator on
  • Automatic stop-start no longer stops the engine
  • Radio or displays may reboot during engine starts

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

P2C44P2C45P2C46P2C47U061EP25FF

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