Powertrain, generic (extended)

P2D66 Battery Charging System Negative Contactor C Control Circuit Range/Performance

Check engine lightUsually off

EmissionsNot relevant

Drive cycleNot required

Limp modeNo

P2D66 flags a coil circuit of minus charging contactor C that is connected but responds outside its expected band while showing neither a break nor a short. P2D66 is not described by any manufacturer, and GM's public tables list no range test for charge contactor coils. A GM patent shows why such a check needs care: the coil current of the same contactor differs markedly between -40, 25 and 85 °C, so the patent compares readings with a reference stored offline for each contactor. CARB requires output parts that a maker monitors on a hybrid to respond properly to commands. Corroded terminals and an aged coil fit this pattern. P2D65 is the open, P2D67/P2D68 low and high, P2D5F the plus side.

Likely causes

Corroded or loose terminals raising circuit resistance

Coil resistance drifted through ageing or overheating

Module software with an unsuitable reference or calibration

Symptoms

Charging via contactor C drops out now and then
Fault occurs mainly in very cold or very hot conditions
Code returns after clearing

Repair estimate

DifficultyShop_onlyWorkshop 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

bcs neg contactor cwiring harnessbms

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