What P0A90 means
P0A90 reports that electric drive motor A does not behave as commanded.
How the engine computer detects it
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.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- MIL and hybrid system warning
- Belt squeal or auto-stop/start not working
- Reduced electric assist or limp mode
Common causes
- Slipping, worn or broken drive belt on belt-driven motor/generators Most likely
- Faulty belt tensioner or contamination on the belt Possible
- Motor, position sensor or inverter fault in full hybrids Possible
How to diagnose P0A90
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: drive motor a.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- A
- Hybrid and electric propulsion
- 90
- Specific fault
Questions drivers ask
Can I drive with code P0A90?
If the car drives normally, drive gently to a shop that services hybrids. If it shows a hybrid system warning, loses power or won't go into Ready, pull over and have it towed. Never touch orange high-voltage cables.
Will my car pass an emissions inspection with P0A90?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Can I fix P0A90 myself?
Often yes, with an OBD-II scanner and basic tools. Difficulty: medium. Start with the cheapest checks before replacing expensive parts.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.