Powertrain, generic · Hybrid propulsion

P0A0B High Voltage System Interlock Circuit A Performance

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

The interlock loop A responds electrically, but its behaviour does not match what the module expects – for example a loop resistance outside the window, a signal that does not follow the commanded test pattern, or two modules on the same loop disagreeing. Mercedes-Benz logs P0A0B00 in the battery management system, the DC converter and the on-board charger of model line 243 when the vehicle will not start; its listed causes include oxidised interlock pins in the low-voltage connectors, twisted or chafed harnesses and bent pins on HV components. Patent literature explains why voltage-based loops are prone to false alarms from contact resistance and interference. Unlike P0A0C/P0A0D this is not a clear short. Expect the HV system to stay off.

Likely causes

Oxidised interlock pins in low-voltage connectors raising loop resistance
Improperly connected HV connector or bent interlock pins on an HV component
Twisted or chafed interlock harness rubbing on the body
Faulty interlock driver or receiver in a control module

Symptoms

  • Vehicle cannot be started
  • High-voltage system warning in the instrument cluster
  • Several modules store interlock codes at the same time

Repair estimate

DifficultyHardWorkshop 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

hv interlock circuit awiring harnessbms

Related codes

P0A0AP0A0CP0A0DP0A0EP0D16

References: static.nhtsa.gov, patents.google.com, law.cornell.edu.