P0A4B

What it means

P0A4B is the SAE J2012 generic code for a fault in the Generator Position Sensor circuit, which is used on hybrid and electric vehicles. The generator (or motor-generator) position sensor, often a resolver, tells the hybrid control unit the exact rotor angle and speed so it can time the drive current correctly. The code sets when the signal is missing, out of range, noisy or implausible compared with expected values.

Symptoms

• Hybrid system warning light or master warning light on
• Reduced power or the car going into a limp mode
• Engine not starting, or the hybrid system not entering ready mode
• Engine running roughly or stalling, with poor or no hybrid assistance
• Poor fuel economy because hybrid functions are limited
• Possible additional hybrid or inverter fault codes stored

Possible causes

• Damaged, chafed or corroded wiring or connector in the generator position sensor circuit (open circuit, short or high resistance)likely
• Faulty generator position sensor or resolverlikely
• Moisture, coolant or oil contamination at the sensor connector or inside the generator housingpossible
• Sensor misaligned or incorrectly fitted after previous repair work to the generator or transaxlepossible
• Electrical interference from damaged shielding or poor earthing affecting the sensor signalpossible
• Fault in the hybrid control unit or inverter that processes the sensor signalrare
• Mechanical damage inside the generator affecting the rotor or sensorrare

How to diagnose

1. Read all stored codes and freeze frame data, noting any other hybrid, inverter or motor codes and the conditions when the fault set
2. Check for manufacturer service information or bulletins relevant to the model, as sensor type and procedures vary by vehicle
3. Visually inspect the sensor wiring and connectors for chafing, corrosion, water ingress, bent pins and poor locking
4. Observe the generator speed and position data on live data while the system is running and look for dropouts or implausible values
5. With the high voltage system safely isolated by a suitably trained technician, test the sensor circuit for continuity, shorts and resistance against the model's specification
6. Check the sensor coil resistance against the manufacturer's values, as these differ between models
7. Check shielding and earth connections on the sensor harness
8. Verify sensor fitment and alignment if the generator or transaxle has been worked on recently

How to fix

• Repair or replace damaged wiring, and clean or replace corroded or damaged connectors
• Replace the generator position sensor or resolver if its readings are out of specification
• Cure any source of moisture or fluid leakage and dry or replace affected components
• Refit or realign the sensor to the manufacturer's procedure, including any required learning or initialisation
• Restore damaged shielding or earth connections
• Replace or reprogram the hybrid control unit or inverter only after the wiring and sensor are proven good and where the manufacturer's diagnosis confirms it

Can I keep driving?

Nearby codes

• P0A4AGenericDrive Motor B Position Sensor Circuit Overspeed
• P0A4CGenericGenerator Position Sensor Circuit Range/Performance