Powertrain, generic · Transmission

P0818 Driveline Disconnect Switch Input Circuit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

P0818 concerns a switch input that reports whether the driveline is disconnected – on four-wheel-drive vehicles typically the neutral position of the transfer case or an axle disconnect, on hybrids a disconnect clutch between engine and transmission, as a Ford patent uses the term. It matters for OBD because in transfer case neutral the engine runs without load and wheel speed does not match the ratio, so misfire, ratio and vehicle speed monitors must know about it; CARB requires monitoring only then. The check would be a circuit or plausibility test against the speed ratio. No manufacturer document available to us uses P0818, and which of the two meanings applies cannot be proven. All-wheel drive or neutral may then be unavailable.

Likely causes

Neutral or disconnect switch at the transfer case or axle faulty
Underbody wiring or connector corroded or damaged
Transfer case actuator does not reach its end position
Control module or software

Symptoms

  • All-wheel drive or neutral cannot be selected
  • 'Service 4WD' or similar warning
  • Possibly check engine lamp (depends on manufacturer)

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–500
Time0.5–2.5 h

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

Parts involved

driveline disconnect switchtransfer caseswitch wiring

Related codes

P0836P0837P0800P0850

References: law.cornell.edu, patents.google.com.