Having problems with your Mitsubishi Galant ?

2001 Mitsubishi Galant. Battery light came on last week. Had alternator replaced. 2 days later, Service Engine light came on and car chugged/lurched. Had tune-up and coil replaced. 3 days later, car chugged and not driveable. Mechanic said coil was defective. Service Engine light back yesterday (2 days later). BTY, Autozone reading was a code PO421, but could this be causing inability to operate vehicle.?

Posted / edited by AnonymousUser on : 22-04-2019

Answers :

The error code p0421 means.Warm Up Catalyst Efficiency Below Threshold (Bank 1).The O2 sensor is to be replaced.\015\012There are two O2 sensors.One is pre- catalytic converter and one is post-catalytic converter.Replace both the O2 sensors.As per the code p0421 it indicates the O2 sensor after the converter.But you replace both the sensors.-----------------also as you mentioned that problem is causing inability to operate vehicle.So in that case i will say,replace both O2 sensors,plus get your MAF sensor also replaced.Also get your cars fuel injectors and spark plugs cleaned.\015\012The MITSUBISHI Galant Mass Air Flow sensor is usually installed in the intake air duct between the air filter and the throttle body mounted on the intake manifold. Some mass air flow sensors are mounted directly to the throttle body.Most probably in your case the MAF sensor needs replacement,because Problems with Mass Air Flow sensors are common. Bad or contaminated MITSUBISHI Galant Mass Air Flow sensor can possibly cause a wide range of various vehicle drivability problems such as stalling, especially when the engine is cold, misfiring, poor acceleration, etc. In addition, a problem with the Mass Air Flow sensor often causes the "check engine" or "service engine soon" light in the vehicle instrument panel to illuminate.\015\012-----------------\015\012This troubleshooting will help to correct the problem. Thanks. Helpmech.
P0421 - Warm Up Catalyst Efficiency Below Threshold (Bank 1)

Basically this means that the oxygen sensor downstream of the catalytic converter on bank 1 is detecting that the converter is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

Symptoms: You will likely not notice any drivability problems, although there may be symptoms. The code may be more likely to occur after the engine has had numerous cold starts in the past 1-2 days.

Causes: A code P0421 may mean that one or more of the following has happened:
* The catalytic converter is no longer functioning properly
* An oxygen sensor is not reading (functioning) properly
* A sparkplug is fouled up

Possible Solutions: Measure the voltage at the oxygen sensor on Bank 1 (the rear sensor, or the sensor after the converter). In fact, it would be a good idea to test each oxygen O2 sensor while you're at it.

One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem.

Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into. Hope this helps; keep us updated.
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