P0A0B: High Voltage System Interlock Circuit A Performance

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.

High severity. Can I keep driving?If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.

Symptoms

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

Most 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

What to check, in order

Start with the simplest. You can tick off each step.

Read the codes with a hybrid-compatible scanner and write down the freeze frame data
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
Make sure the battery cooling air intake is clean
Check the 12 V auxiliary battery, which can also trigger warnings
Leave any high-voltage measurements to a specialized repair shop

Good to know

Repair difficulty: hard
It can trigger limp mode.

What each character of P0A0B means

P: Powertrain: engine and transmission
0: Generic code: same on every make
A: Hybrid or air and fuel
0B: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0A0B?

If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.

What causes code P0A0B?

The most common causes are: 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.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.