Blip of the Check Engine Light

CaptainXL

Original poster
Member
Dec 4, 2011
2,445
For the record I was driving to Detroit this past week and noticed about 100 miles into the trip that the CEL came on once for about 1/4 of a second. Never noticed any issues the rest of the 375 mile trip back and forth. Scan tool noted no codes or any other problems.

The only thing I did prior to the trip is empty out the gas in the garage which was used for the snow blower. None of them had a 2 cycle mix but it was winter blend fuel.

It's probably nothing but just thought I would note it here in the forums.
 

Ryda55555

Member
Apr 11, 2013
1,111
CaptainXL said:
For the record I was driving to Detroit this past week and noticed about 100 miles into the trip that the CEL came on once for about 1/4 of a second. Never noticed any issues the rest of the 375 mile trip back and forth. Scan tool noted no codes or any other problems.

The only thing I did prior to the trip is empty out the gas in the garage which was used for the snow blower. None of them had a 2 cycle mix but it was winter blend fuel.

It's probably nothing but just thought I would note it here in the forums.

That was happening to me too on long trips, pop on for fast enough for me to see then off. it eventually stayed on long enough for me to catch my thermostat dying
 

CaptainXL

Original poster
Member
Dec 4, 2011
2,445
Well for anyone that has been following my quirks, I have suspected it as well. My engine has been slow to heat up the past winter. I had a long thread about this a few months back. I will be changing it within a few weeks as a preventative maintenance thing. It's been three years since the thermostat was replaced.
 

Ryda55555

Member
Apr 11, 2013
1,111
CaptainXL said:
Well for anyone that has been following my quirks, I have suspected it as well. My engine has been slow to heat up the past winter. I had a long thread about this a few months back. I will be changing it within a few weeks as a preventative maintenance thing. It's been three years since the thermostat was replaced.

My grammar in the last post was terrible lol i was multitasking at the time hahaha
But yea it doesnt hurt to change if you dont mind the work involved
 

Blckshdw

Moderator
Nov 20, 2011
10,694
Tampa Bay Area, FL
Mine's been doing that for a couple of years now, never any codes either. I've had a bunch of under hood stuff replaced under warranty, for other issues, but this remains. The times I tend to notice it more frequently is in slow moving traffic, as that's when I tend to check my gauges and such the most. 90% of my driving is city.
 

DARKASS04EXT

Member
Nov 21, 2011
193
My 04 EXT has been doing this for years. I tried to get some help while still on TV awhile back but nothing ever came of it. It actually just happened over this past weekend, never any codes etc... I just call it my "phantom" light.
 

seanpooh

Member
Jan 24, 2012
461
This does happen to me on occasion. If I don't run any lucas fuel injector cleaner or chevron techron for a good couple thousand miles, the CES come on. Same goes for my brother's Saturn Vue. I happen to drive with a scanner and it always states that the catalytic convertor is not up to threshold.

Run some injector cleaner in the tank and it goes away in less than 20 miles. I assume it happens with bad batches or long rides, something builds up and give a reading the computer doesn't like.
 

CaptainXL

Original poster
Member
Dec 4, 2011
2,445
seanpooh said:
This does happen to me on occasion. If I don't run any lucas fuel injector cleaner or chevron techron for a good couple thousand miles, the CES come on. Same goes for my brother's Saturn Vue. I happen to drive with a scanner and it always states that the catalytic convertor is not up to threshold.

Run some injector cleaner in the tank and it goes away in less than 20 miles. I assume it happens with bad batches or long rides, something builds up and give a reading the computer doesn't like.

I think we are discussing separate things. I never had any code as you did for P0420 (catalytic converter efficiency).

Check for other codes as the P0420 is the end result of something wrong. In this case check fuel trims. They could be way off.

With the engine at operating temperature look at the front and rear O2 sensors on a scan tool with the rpm around 2200. If the rear O2 sensor is mimicking the front one, the converter will most likely need to be replaced. Usually if you are getting a P0420 then the catalytic converter is not converting HC's into H2O and CO2. The P0420 will not show if the PCM detects that the oxygen sensors are bad and throws a code for them. The converter efficiency test is done by the PCM and it depends on good O2 sensors.

A less scientific test for this condition is to stick your nose in the exhaust after the engine is fully warmed up and held at 2200 rpms and take a couple whiffs. If there is little smell then the converter is doing it's job.

Now, as to the reason for the P0420. It's no joke that too rich of a mixture will carbon foul a converter. That is why we are always on the lookout for any early symptoms of failed thermostat or coolant temp sensors. I would also be wary of excessive engine wear and oil consumption which could also foul the cat.

For a more detailed explanation see The Misleading Nature of the PO42O Code - Eastern Manufacturing
 

seanpooh

Member
Jan 24, 2012
461
Sorry for the mix up. I assumed the SES light appearing and going away on it's own was because of carbon buildup. Just a little fuel injector cleaner does the trick. Maybe not in this case, never an easy fix...
 

CaptainXL

Original poster
Member
Dec 4, 2011
2,445
seanpooh said:
Sorry for the mix up. I assumed the SES light appearing and going away on it's own was because of carbon buildup. Just a little fuel injector cleaner does the trick. Maybe not in this case, never an easy fix...

Hey Sean, I would check your exhaust backpressure and O2 sensor readings. Never know what you will find. I bought one of those exhaust pressure gauges and I had 0 psi at both idle and 2200 - 2500 rpm. Perhaps your cat is really partially clogged? That's what I was referring too. After reading a bit I have found that the P0420 light will illuminate if the efficiency is down even a relatively small percentage. say 10% or so. Like I was saying, what might be happening is you have a leaking fuel injector which sounds likely since an application of fuel injector cleaner seems to solve it for a bit. I can't imagine how fuel injector cleaner would help the cat after it is burned up. But if the injector is stuck and then fixed for a short period the cat could be ridding itself of some of the carbon in the mean time before the leaking injector repeats again.
 

khill

Member
Jan 7, 2012
86
Mine's had the phantom CEL blip for years too without any seemingly possible cause. On occasion, though, this will occur while braking and while the CEL blips on, the pedal will shake as well as if ABS is going nuts. Haven't seen any ill effects yet.
 

DocBrown

Member
Dec 8, 2011
501
Bad air can cause this to happen too. I know that sounds ridiculous but what I'm saying is that if the truck breaths in air that's heavy with some pollutant it can cause downstream issues with sensors. After everything burns off it goes away. A few years ago we towed on I90 through Montana. There were fires east of Bozeman and enough smoke in the air to make you close the windows. The smoke triggered a CEL. It went away after we got to Yellowstone. It came back on during the return trip and cleared again in South Dakota.
 

DenaliHD66

Member
Dec 4, 2011
597
CaptainXL said:
For the record I was driving to Detroit this past week and noticed about 100 miles into the trip that the CEL came on once for about 1/4 of a second. Never noticed any issues the rest of the 375 mile trip back and forth. Scan tool noted no codes or any other problems.

The only thing I did prior to the trip is empty out the gas in the garage which was used for the snow blower. None of them had a 2 cycle mix but it was winter blend fuel.

It's probably nothing but just thought I would note it here in the forums.


Happens to me too. The first ever time it ended up being thermostat. Sometimes I notice it will do it when shifting from 1st to 2nd while coasting. Hasn't done it with my new transmission yet though.
 

blazinlow89

Member
Jan 25, 2012
2,088
I have seen it pop up randomly for the last 2-3 years. Last time it stayed on I got an error for the CPAS. Cleaned when I did the next oil change and that light never came back.
 

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