P0ADD: Hybrid/EV Battery Negative Contactor Control Circuit/Open

The negative main contactor closes the return path of the traction battery; P0ADD reports an open in its coil drive circuit. GM documents the code in parallel to the positive side: tables since model year 2011 detect open load in the HPC2 and store it after two trips; 2016-19 tables evaluate a control voltage between 1.15 and 2.81 V while off, 40 of 50 samples, Type B, and 2019 tables add a coil current check below 194 mA when on. CARB 1968.2 covers this circuit monitoring of hybrid components. Related codes are P0ADF and P0AE0 for low and high, P0AA5 for a contactor stuck open, P0AD9 for the positive side. Without this contactor the HV system stays 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 will not enter ready mode or start
Hybrid or EV warning light and check engine light
Charging not possible

Most likely causes

Open in negative contactor coil or its pigtail
Loose or corroded connector at the battery disconnect unit
Broken control wire in the battery harness
Driver in the battery controller defective

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 continuity of the wire between the component and the control module.
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

It can trigger limp mode.
It affects emissions.

What each character of P0ADD means

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

Frequently asked questions

Can I keep driving with code P0ADD?

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 P0ADD?

The most common causes are: open in negative contactor coil or its pigtail; loose or corroded connector at the battery disconnect unit; broken control wire in the battery harness.

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.