Powertrain, generic (extended)

P263B MIL Control Circuit High

Check engine lightUsually off

EmissionsRelevant

Drive cycleNot required

Limp modeNo

P263B is stored when the MIL control line is stuck at supply voltage while the module has switched its driver on to light the lamp. GM treats an impedance toward power of about 0.5 ohm as the fault and needs 4 failures within 5 samples, each 50 ms apart, provided run/crank voltage is at least 11 V and no remote start is running. As with P263A, GM labels the code Type B with no MIL, because a shorted control circuit cannot reliably show the warning. In practice the indicator stays dark even when other emissions faults are present, which is why reading stored codes matters, also before an emissions inspection. GM's PIT5391 bulletin ties P263B on 2014–2016 full-size trucks and SUVs to a missing ignition 1 supply. Check the cluster wiring and the driver output.

Likely causes

MIL control wire shorted to a positive feed

Ignition 1 supply interrupted at relay or fuse block

Lamp driver in the engine module failed

Symptoms

Engine warning lamp does not light, not even at key-on bulb check
Other emissions codes stored without warning

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€40–500

Time0.5–2 h

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

Parts involved

mil lampinstrument clusterwiring harness

Related codes

P263A P0650

References: gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov.