Skip the auto shop - Our mechanics make house calls

Q: My car shows a P0420 code and the engine coolant temperature reading (via torque pro app and elm327 Bluetooth reader) stayed at 84.2 degrees

asked by on

How low can the ect read, I'm pretty sure a faulty ect is my issue that or an o2 sensor, because the cataylist should still be fine with the mileage on this car, but I have not ruled it out completely, car was parked for roughly 5 hrs before checking then I first done KOE to get code, cleared and monitored PIDs with engine running approximately 5 min (I feel the owner of the car has been swindled by a shop) Thanks

My car has 90000 miles.
My car has an automatic transmission.

A: Hi there - "boundary measured engine t...

Hi there - "boundary measured engine temperature," or the lowest temp reading a sensor can transmit, can be different based on each temperature sensor. The issue here is what is the true engine temperature? Is the thermostat getting the engine up to its design temperature (something near 205 degrees Fahrenheit/100 Centigrade). Can you cross-check the engine temperature with a laser thermometer, cockpit temperature gauge (middle of the gauge usually), or other measuring device? If the engine is truly coming up to 200 degrees (F) or so, then yes, the ECT can read "low" to the computer, causing rich mixture running. This could cause a low catalytic converter efficiency problem if the engine has run rich for a while.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%

Get a quote

What others are asking

Q: Need to replace the broken alternator on my car with a salvaged part

Alternators will generally have their current rating printed on a label on the back of the alternator. You will want to select one with an equal or higher rating than the one you are replacing. Always make sure the battery...

Q: Headlights won't turn off

Something like this is usually caused by a faulty headlight switch or a shorted wire going to the headlights. The source of the problem needs to be inspected so I would recommend having this looked at by a mechanic so...

Q: Car overheats, heater malfunction

I'm not real clear yet on what is going on with your Mazda. Let's start with the diagnosdtic trouble code (DTC) that indicated a faulty Engine Coolant Temperature sensor. That needs to be replaced. Next thing: you may want to...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...