P20E7Reductant Injection Air Pressure Sensor Circuit Intermittent/Erratic
The signal from the reductant injection air pressure sensor is cutting in and out or jumping erratically instead of changing smoothly.
Definition
The control module on air-assisted SCR systems continuously samples the reductant injection air pressure sensor and expects gradual, plausible changes. P20E7 sets when the signal is intermittent or erratic, momentarily dropping out or spiking faster than physical pressure can change, which almost always indicates a connection or wiring fault rather than a pressure problem. Intermittent readings can interrupt DEF dosing, raising NOx emissions, setting the MIL, and eventually triggering inducement derates on trucks that enforce them.
Common causes
- Loose, corroded, or backed-out terminal in the sensor connector
- Chafed harness making intermittent contact with ground or voltage
- Failing sensor with an intermittent internal element
- Vibration damage to wiring near the dosing module
- Poor pin tension after previous connector service
Common misdiagnoses
- Sensor replaced when a connector terminal has lost tension
- DEF dosing module replaced for a wiring intermittency
- Air supply solenoid replaced chasing erratic pressure readings
- NOx sensor replaced for downstream efficiency codes it caused
Troubleshooting steps
1.Graph the sensor PID while wiggle-testing
Flex the harness and tap the connector while watching a graphed PID; any instantaneous dropout marks the fault location.
2.Inspect connector terminals
De-pin and check terminal tension with a test pin; a terminal that slides on with no drag needs replacement.
3.Check harness routing and chafe points
Trace the loom near brackets and heat shields for rubbed-through insulation making intermittent contact.
4.Monitor over a road test
Record the PID during a drive with bumps and engine torque changes to catch vibration-dependent faults.
5.Replace the sensor if wiring proves sound
Confirm the fix with an extended recording showing a smooth, plausible pressure trace during dosing.