P20BA - Reductant Heater 'A' Control Circuit Performance
System
Powertrain (Engine & Gearbox)
Technical Description
The control module has detected a fault in the Reductant Heater 'A' Control Circuit Performance (P20BA).
Multimeter Test Points & Nominal Values
| Test Point / Component | Measurement | Nominal Target Range | Test Condition |
|---|---|---|---|
| Reductant Heater 'A' Control Circuit Performance – Coil Resistance | Resistance (Ω) | 3 - 30 Ω (typical) | Connector disconnected at 20°C |
| Reductant Heater 'A' Control Circuit Performance – Duty Cycle | PWM (%) | 5 - 95 % (modulates with target) | Engine running, actuator in control |
| Reductant Heater 'A' Control Circuit Performance – Supply Voltage | Voltage (V) | 11.8 - 14.4 V | Ignition ON at connector |
Connector disconnected at 20°C
Engine running, actuator in control
Ignition ON at connector
Oscilloscope Waveform Analysis
2 ms/div, 20 V/divPossible Causes
Reductant Heater 'A' Control Circuit Performance is electrically operational but performing outside calibrated tolerance
Channel A:Verify dedicated wiring pins and signal pair for circuit A against the schematic.
Chafed or pinched wiring harness along the signal path to Reductant Heater 'A' Control Circuit Performance
Internal mechanical wear or carbon deposits inside Reductant Heater 'A' Control Circuit Performance
Defective internal output driver or reference circuit in the control module for Reductant Heater 'A' Control Circuit Performance
Symptoms
Recommended Solution
Compare signal voltage and resistance between circuit A and companion circuit B at module connector.
Verify underlying mechanical operation and rule out blockage, vacuum leaks, or mechanical binding.
Verify loaded supply voltage and harness terminal pins at Reductant Heater 'A' Control Circuit Performance.
Check circuit continuity and ground-side voltage drop (< 0.05 V) for Reductant Heater 'A' Control Circuit Performance.
Check supply and the low-side driver at the ECM connector. Replace the actuator or repair the circuit based on the readings.
Mechanic's Tip
Use the scan-tool output test with the scope on the control side at the same time. If duty changes but the actuator does not move, the valve is stuck — not the electrical fault you were chasing.