What Does P0AF4 Mean?
The motor controller has detected that drive motor inverter temperature sensor B circuit voltage is below the minimum expected threshold. Low voltage on an NTC thermistor circuit indicates very low resistance, which means either the sensor is shorted, there is a wiring short to ground, or the inverter is genuinely at an extreme temperature. The controller will interpret this as a critical over-temperature and take aggressive protective action.
Safety Warning
The controller will severely limit or shut down the electric drive in response to this fault. If the fault is a genuine over-temperature, continued driving risks permanent inverter destruction. If it is a sensor fault, the vehicle will be unnecessarily disabled. In either case, do not override protective measures — have the system inspected promptly.
Common Causes
30%
Internally shorted NTC thermistor (failed to near-zero resistance)
30%
Short to ground in the sensor B wiring harness
20%
Moisture or coolant contamination at the sensor B connector
15%
Genuine over-temperature at the inverter phase module monitored by sensor B
5%
Motor controller analog input failure pulling signal low
Diagnostic Steps
1
Read inverter temperature B value — if extremely high (above 100C) while the vehicle has not been under heavy load, the cause is electrical rather than thermal.
2
Disconnect sensor B and measure its resistance. Near 0 ohms indicates a shorted sensor. Normal NTC at 25C is 5K-50K ohms.
3
With sensor B disconnected, measure insulation resistance from each wire to ground. Less than 100K ohms indicates a short to ground in the harness.
4
Inspect the sensor B connector for moisture, coolant leaks, or corrosion. Inverter coolant leaks can contaminate nearby electrical connections. Clean, dry, and apply dielectric grease.
5
If genuine over-temperature is suspected, compare sensor A's reading, check coolant flow through the inverter, and inspect the IGBT module for signs of thermal damage (discoloration, warping).
Estimated Repair Cost
$150 - $1,800
Parts + labor, varies by vehicle and location
The motor controller has detected that drive motor inverter temperature sensor B circuit voltage is below the minimum expected threshold. Low voltage on an NTC thermistor circuit indicates very low resistance, which means either the sensor is shorted, there is a wiring short to ground, or the invert...
The most common cause of P0AF4 (Drive Motor Inverter Temperature Sensor "B" Circuit Low) is: Internally shorted NTC thermistor (failed to near-zero resistance)
Typical repair costs for P0AF4 range from $150 to $1,800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The controller will severely limit or shut down the electric drive in response to this fault. If the fault is a genuine over-temperature, continued driving risks permanent inverter destruction. If it is a sensor fault, the vehicle will be unnecessarily disabled. In either case, do not override protective measures — have the system inspected promptly.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0AF4 to identify the root cause.
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Quick Info
Category
Powertrain
System
Hybrid/EV Drive Motor & Inverter
Difficulty
Type
Generic (SAE)
Recommended Tools
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