QuestionMy Santa Fe has 76k miles on it and recently had the check engine light come on. The codes I recieved were P0421, P0401, and P0442, all exhaust or emission issues. Could they all be tied to the catalytic converter? Any other reccomendations for a do it yourself project would be very much appreciated.
Thank You
AnswerThese are not all tied to the catalytic converter.
P0401 indicates an abnormal EGR flow. The easiest way to test the majority of EGR components at one time is to pinch closed the yellow-striped vacuum hose at the throttle body. This mimics closing of the EGR solenoid and should cause the EGR valve to open an the engine to idle poorly. If it does, you've just verified that the vacuum hoses are attached and intact, the EGR valve functions normally, and the passage in the intake is not clogged. In this case, the problem is with the EGR solenoid or the vacuum bleed-off valve (called a vacuum switch by Hyundai). Potentially, you could have an EGR problem created by a clogged converter causing excessive backpressure, but if this is the case, the vehicle should run so bad that it's almost not driveable.
P0421 almost certainly indicates the manifold catalytic converter is not working properly. If you can verify that the oxygen sensors are attached to the proper connectors and are working properly, then you'll need to replace the manifold catalytic converter.
P0442 indicates a small evaporative emissions leak. To test the system, the engine control module (ECM) closes the canister close valve (at the canister) and uses engine vacuum through the purge control valve to draw a vacuum on the system. The ECM then closes the purge control valve and monitors the rate of vacuum bleed-off. If the vacuum bleed-off is sufficient to indicate a small leak, the code P0442 is set.
