Our car has the check engine light come on with a codes P0401 and P0122. The car seems to run fine. What sorts of things should we check?


2 Answers 2


DTC P0122 Throttle postion sensor (TPS) switch A circuit low input

Possible causes include:

  • Poor connection
  • Open or short to ground
  • Faulty TPS
  • Faulty PCM

DTC P0401 EGR flow insufficient

Possible causes include:

  • Faulty EGR vavle
  • Fauty PCM

P0122. The throttle position sensor of your vehicle can be checked with a graphing scanner. Voltages and operation can be watched from the comfort of the drivers seat. The voltages of the terminals can be further checked with a voltmeter on the wiring for correct voltages or shorts.

P0410. The EGR has a vacuum operated valve which needs to be checked for holding its vacuum. The EGR operation can be checked with a suitable scanner with bi-directional controls. EGR valves have a deserved reputation for being troublesome because of their handling of the exhaust gases causes clogging and seizing. Staying open and staying closed.

Hyundai have a web site, HMAservice.com, which covers their service routines, TSB's and a whole lot more. At this time it is free to access.

It appears to me that your EGR valves operating valve is not opening the EGR valve and the throttle switch is reporting the higher then expected manifold vacuum as a voltage error.

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