Q: Check engine light on, error code P0300, P0302, P0171,

asked by on

Check engine light is on, steady most of the time, but sometimes, the check engine light flashed for a short while then turned steady again after I slow down. If I drive only 30 miles/hr or under, check engine light remained steady, no flashing.

All 4 spark plugs and ignition coil #2 were replaced today, it did not help. Should I still drive the car at about 30 miles/hr until a friend helped to change the up stream oxygen sensor free. It would take another month before this friend has time. Thank you !

My car has 124500 miles.
My car has an automatic transmission.

Hi there. Why are you going to replace the O2 sensor? Did testing reveal a problem with the sensor itself? It sounds like there could be an air leak concern or an airflow meter concern. Has anyone checked for cracked, leaking, or loose vacuum hoses? Has the airflow meter been tested against specifications? Pull the airflow meter out and check the self cleaning wire element to see if one side is covered and not clean, if not then replace the meter and recheck operation; inaccurate airflow readings can create misfires. I suggest having a qualified technician perform an inspection to avoid replacing unnecessary parts. Your Mechanic has several technicians available that can assist you with a check engine light inspection.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1,000 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
  1. Home
  2. Questions
  3. Check engine light on, error code P0300, P0302, P0171,

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: What does the headlight control sensor do?

If your car has automatic headlights, then it also has a headlight control sensor. Essentially, this is what’s responsible for turning your headlights on and off based on ambient light levels. The sensor is located on the dash near the...

Q: Quesiton

If the part listed is a genuine Toyota oil filter, it is very likely that the oil filter is the same one they would use at the dealership. This tends to be the highest quality available. It would meet the...

Q: Q: How do I tilt the moon roof?

The moon roof tilt is controlled by the moon roof switches, which are directly in front of the moon roof, on the ceiling. To tilt the moon roof open, press the TILT button once. To close the tilt, press the...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
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...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...