Engine Light On

OooWeee428 · #1 (**permalink**) 09-26-2003, 11:39 PM

The check engine light on my truck went on while i was driving and i have no idea why. The truck still runs fine and i checked the level on my oil and that's fine too. Any suggestions to why its like this???

v8Toilet · #2 (**permalink**) 09-26-2003, 11:45 PM

Quote:

Originally Posted by OooWeee428

The check engine light on my truck went on while i was driving and i have no idea why. The truck still runs fine and i checked the level on my oil and that's fine too. Any suggestions to why its like this???

Might be an 02 sensor failing. They can go anywhere from 30,000 miles to 60,000 miles, which is about how long they last. Go to autozone and have them read the code to tell you what it might be.

OooWeee428 · #3 (**permalink**) 09-26-2003, 11:49 PM

Thanks! I have somewhere near 45000 miles on my truck too. By the way if it is my O2 sensor is the truck still safe to drive cause i probably can't get it checked till Monday. Also how much is the cost to replace the sensor.

v8Toilet · #4 (**permalink**) 09-26-2003, 11:54 PM

Quote:

Originally Posted by OooWeee428

Thanks! I have somewhere near 45000 miles on my truck too. By the way if it is my O2 sensor is the truck still safe to drive cause i probably can't get it checked till Monday. Also how much is the cost to replace the sensor.

They cost $$$ at the dealer but you can get them @ www.sparkplugs.com for $50 and they are Denso 02 sensors or what you have now. It’s OK to drive it with the check engine light on.

beemerphile · #5 (**permalink**) 09-27-2003, 09:25 AM

Quote:

Originally Posted by v8Toilet

It’s OK to drive it with the check engine light on.

True that it's OK for a little while, but don't let it go too long. If it is one of the primary O2 sensors, the computer will run in "limp home" mode with richer than nomal mixture. If you run this way long enough, you will damage the catalytic converter. THEN you will be spending some serious jack. - Lee

arkie6 · #6 (**permalink**) 09-27-2003, 10:55 AM

Quote:

Originally Posted by beemerphile

True that it's OK for a little while, but don't let it go too long. If it is one of the primary O2 sensors, the computer will run in "limp home" mode with richer than nomal mixture. If you run this way long enough, you will damage the catalytic converter. THEN you will be spending some serious jack. - Lee

Almost every check engine light issue relating to O2 sensors posted on this site to date has been due to a malfunction of the O2 heater circuit, not the O2 sensor itself. A malfunctioning O2 heater circuit will not force the ECU to go into open loop mode under normal driving conditions because the O2 sensor is still functional when hot. The only problem I can see from this condition is that it may take a little longer for the O2 sensor to heat up which will delay the ECU from going from open loop mode (ignores O2 sensors) when first started to closed loop mode when in normal operation (lowest emissions).

My truck has been operating just fine for close to 6 months with a check engine light as a result of a O2 sensor heater circuit failure. I have noted no change in performance or fuel economy and I check the MPG on every fill up.

I do agree that it is still a good idea to get the check engine light investigated to find out what is causing the light. If it is just the O2 sensor heater circuit failure, then no harm is being done to the engine or catalytic converters in my opinion.

OooWeee428 · #7 (**permalink**) 09-27-2003, 10:00 PM

thanks guys i'm not freaking out as long as i was anymore. But i will for sure get it checked on monday

LGL002 · #8 (**permalink**) 09-28-2003, 09:32 PM

I thought California emission rules required a longer factory warranty on o2 sensors sold in the State. Shouldn't make any difference if you aren't the original owner

OooWeee428 · #9 (**permalink**) 09-28-2003, 10:18 PM

OK! Now i'm confused cause my dad was driving the truck yesterday to see if there was anything wrong with it then suddenly the check engine light went off. What am i supposed to think now???

v8Toilet · #10 (**permalink**) 09-28-2003, 10:47 PM

Quote:

Originally Posted by OooWeee428

OK! Now i'm confused cause my dad was driving the truck yesterday to see if there was anything wrong with it then suddenly the check engine light went off. What am i supposed to think now???

If you don’t tighten the gas cap all the way until it clicks you could get a mill light because the evaporative emissions systems won’t hold pressure.

OooWeee428 · #11 (**permalink**) 09-28-2003, 10:50 PM

So do you think that it was just my gas cap cause my dad did just fill up my tank yesterday.

ske · #12 (**permalink**) 10-12-2003, 01:31 AM

Quote:

Originally Posted by OooWeee428

OK! Now i'm confused cause my dad was driving the truck yesterday to see if there was anything wrong with it then suddenly the check engine light went off. What am i supposed to think now???

I was just as confused when the same thing happened to me the other day. When I got home I cracked open the repair manuals and found out there are a couple of fail safe systems in place.

First, you will not get a (MIL) malfunction indicator lamp or "check engine light" for a malfunctioning emision control system unless the computer detects this for 2 trips. Meaning the malfunction has to occur twice with the ignition being shut off between them.

Second, If you continue driving the vehicle and the computer does not detect the malfunction for 3 consecutive trips the MIL will go out.

This happened to me and now the light is back on which sounds to me like its a sporadic failure. I had the code checked at a local shop today - P0155 "Oxygen sensor heater circuit malfunction". Im going to check with the dealer on Monday to see if its covered under the emision control warranty since im at 43k. If not I'll replace it myself. Hope this helps.

evad3257 · #13 (**permalink**) 11-30-2003, 09:03 PM

hey arkie6,

I am confused. Are you saying that the heater circuit is a different part than the o2 sensor, or are they combined. I understand driving without the heater circuit working properly won't hurt, but will replacing the sensor cure the heater circuit, and therefore, the MIL?

Thanks.....

JeffD · #14 (**permalink**) 12-01-2003, 10:47 AM

The heater circuit is built into the o2 sensor and can't be replaced seperately. I don't know if it detects the fault by seeing an open circuit, or if it sees that it takes too long before it gets a good signal from the O2 sensor.

arkie6 · #15 (**permalink**) 12-01-2003, 01:05 PM

Quote:

Originally Posted by evad3257

hey arkie6,

I am confused. Are you saying that the heater circuit is a different part than the o2 sensor, or are they combined. I understand driving without the heater circuit working properly won't hurt, but will replacing the sensor cure the heater circuit, and therefore, the MIL?

Thanks.....

What Jeff said above. The oxygen sensor and oxygen heater circuit are electrically separate, but physically integrated into a single device. That is why our O2 sensors have 4 wires - 2 for the O2 sensor and 2 for the heater circuit. Can't replace one without the other.