P20E6Reductant Injection Air Pressure Sensor Circuit High
The sensor that measures compressed-air pressure in the air-assisted DEF (reductant) injection system is reading above its valid electrical range.
Definition
On air-assisted SCR systems, common on medium- and heavy-duty diesels, compressed air atomizes diesel exhaust fluid at the injection nozzle, and a pressure sensor lets the control module verify and regulate that air supply. P20E6 sets when the sensor signal exceeds its high electrical limit, indicating a short to voltage, an open ground, or a failed sensor rather than a real pressure condition. DEF dosing may be suspended, which raises NOx output, illuminates the MIL, and on many trucks starts an emissions-related derate or speed-limit strategy if left unrepaired.
Common causes
- Sensor signal wire shorted to reference or battery voltage
- Open sensor ground circuit
- Failed reductant injection air pressure sensor
- Corroded or moisture-contaminated connector
- Harness damage near the dosing module or frame rail
Common misdiagnoses
- DEF injector/dosing valve replaced for an electrical sensor fault
- Air control solenoid replaced when the sensor circuit is at fault
- Complete dosing module replaced without pinpoint testing
- NOx sensors replaced because NOx efficiency codes followed
Troubleshooting steps
1.Read the air pressure PID key-on
A value pegged at maximum with the air system off confirms an electrical high-circuit fault.
2.Disconnect the sensor and watch the PID
If the reading remains pegged, trace the harness for a short to voltage; if it drops, suspect the sensor itself.
3.Verify reference voltage and ground
Check for 4.9-5.1 V reference and a ground drop under 0.1 V at the sensor connector.
4.Inspect the harness and connector
Look for chafing against the dosing unit bracket, green corrosion on terminals, and moisture in the connector seal.
5.Replace the sensor and confirm dosing
Run the SCR system test with a scan tool and verify air pressure reads within the specified dosing window.