P0A90: Drive Motor A Performance

P0A90 reports that electric drive motor A does not behave as commanded. In GM's eAssist mild hybrid the motor/generator is belt-driven from the crankshaft, so GM uses P0A90 to detect a slipping or broken belt: the motor speed is compared with the engine speed. In 2013 a difference above 1000 rpm for 1.5 s, or repeated smaller slips above 500 rpm on two key cycles, set it; the 2016 tables use more than 1500 rpm for about 5.6 s or repeated 1000 rpm slip events. GM rates it Type A, MIL on the first trip. In full hybrids the generic definition applies to speed or torque deviations of the traction motor. P0A91 is the equivalent for motor B, P0A92 for the generator.

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

MIL and hybrid system warning
Belt squeal or auto-stop/start not working
Reduced electric assist or limp mode

Most likely causes

Slipping, worn or broken drive belt on belt-driven motor/generators
Faulty belt tensioner or contamination on the belt
Motor, position sensor or inverter fault in full hybrids

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
Compare the reading with other engine data while varying the engine speed.
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: medium
It can trigger limp mode.
It affects emissions.

What each character of P0A90 means

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

Frequently asked questions

Can I keep driving with code P0A90?

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 P0A90?

The most common causes are: slipping, worn or broken drive belt on belt-driven motor/generators; faulty belt tensioner or contamination on the belt; motor, position sensor or inverter fault in full hybrids.

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.