P0A70: Generator Phase U Current Low

P0A70 means phase U of the hybrid generator carries or reports too little current while the generator is loaded, typical of an open phase or a sensor stuck near zero. No manufacturer documents P0A70 publicly. The closest published test is GM's open-phase check for the drive motors (P0A67 and siblings), which compares the peak current near each phase axis against a 9 A threshold; GM publishes no such test for the generator. A Caterpillar patent identifies a failed phase sensor by a reading close to zero while the currents no longer sum to zero. CARB requires circuit monitoring of electric drive components. P0A71 is the high side, P0A73 and P0A76 phases V and W, P0A6F the general code. Engine start and charging can be affected.

Symptoms

• Hybrid warning and MIL
• Engine runs rough at start or battery charge level keeps dropping

Most likely causes

• Open circuit in the generator phase U lead or terminal
• Generator phase U current sensor stuck near zero
• Phase U switch in the generator inverter not conducting

What to check, in order

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

1. Measure the voltage with the engine off and running
2. With the connector unplugged, check whether the signal wire is making contact with ground.
3. Clean and tighten the terminals
4. Check the accessory belt
5. Run a battery load test
6. Check the alternator wiring

Good to know

• It can trigger limp mode.
• It affects emissions.

What each character of P0A70 means

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

Frequently asked questions

Can I keep driving with code P0A70?

If the battery warning light comes on, you could get stranded. Turn off electrical accessories and go straight to a repair shop.

What causes code P0A70?

The most common causes are: open circuit in the generator phase U lead or terminal; generator phase U current sensor stuck near zero; phase U switch in the generator inverter not conducting.

Related codes

• P0A6FGenerator Phase U Current
• P0A71Generator Phase U Current High
• P0A73Generator Phase V Current Low
• P0A76Generator Phase W Current Low
• P0A67Drive Motor B Phase U Current Low

Sources

• patents.google.com: en
• patents.google.com: en
• law.cornell.edu: 13 CCR 1968.2

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.