Check the 'Possible Causes' listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.
The cost to diagnose the P20A3 code is 1.0 hour of labor. The diagnosis time and labor rates at auto repair shops vary depending on the location, make and model of the vehicle, and even the engine type. Most auto repair shops charge between $75 and $150 per hour.
In order to reverse the reductant flow direction (for line purge) a 4-2-way valve (reverting valve) needs to be switched. The valve is switched by a solenoid.
The reverting valve functional check monitors the pressure drop when the purge cycle is started. To run this test the pressure level must exceed a calibration threshold (280 kPa) at beginning of test. For a successful test result, the pressure must drop by another threshold (230 kPa) within the time.
If the test is not successfully passed the purge cycle will be terminated immediately because of the risk of uncontrolled injection of reductant into the exhaust pipe.
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