Powertrain, generic · Hybrid propulsion

P0B8C Hybrid/EV Battery Voltage Sense Q Circuit Range/Performance

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

P0B8C is set when channel Q reports a voltage that fails the plausibility test against the other cells or the pack. On GM's 2012 two-mode trucks Q is NiMH block 17; the battery pack control module takes block 17 and block 18, multiplies each by twenty and compares with the measured pack voltage, failing beyond 70 V in 160 of 170 samples, Type B. GM's lithium-ion programs instead check that cell Q follows the average: the 2016 Volt within 7 of 8 seconds, the Cadillac ELR in 20 of 40 samples, the 2019 controllers in 35 of 40 samples with a 0.005 V trend, all Type A. Because the value itself is within limits, the driver may notice little beyond the MIL. A software update or replacement of the monitoring electronics resolves most cases.

Likely causes

Monitoring electronics misreading channel Q

Outdated battery controller software

Block 17 or 18 voltage deviating on two-mode NiMH packs

Symptoms

MIL with little change in driving
Usable battery capacity reduced

Repair estimate

DifficultyShop_onlyWorkshop job

Parts and labour€80–5,000

Time0.5–6 h

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

Parts involved

hv battery voltage sense qwiring harnessbms

References: gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com.