Flashing Check Engine Light
 

As soon as I start driving at about 20 k.m/hr my check engine light (CEL) starts blinking . When I put it into park goes away. Most times I don't even get a solid CEL error show up and other times, there are errors but no solid CEL. Most seem to be nothing related to the problem like u1128 entertainment lost comes or u1026 lost comm with transmission , P0455 large evaporator leak, but someone forgot to put the gas cap backnon after fueling up.

I had issues with B1S2 errors and after replacing the sensor twice and finally using a Bosch sensor I seemed to lose the errors on that,

But what I did notice using my bluedriver is my MAF sensor shows around 10 to 12 g/s when starting and even after idle until the engine is warmed I know this is high, no errors on the MAF but I swapped it out with a A Premium part and got the exact same numbers, when I first tried to start it would not even catch just turned over and over, I disconnected theb battery and reset the CEL and it started but same numbers 10 to 11 on idle and up around 20 g/s when driving slow like 20 to 40 km.

I,ve looked at my B1S1 AND B1B2 voltage abd the seem to be different like .445 b1s1 and .830 b1s2 I'm thinking my cats are ok ? I can look at short fuel trim but I'm not sure what I'm looking for my sensor 1 always seems to show NA for either side B1 or B2. The sensor 1 on both sides seem to jump around feom either -6 to +6,

Not sure if I should try another MAF sensor like the Delphi one which nissan about 3 tines the cost

Any advice what i should be looking at here ?
2006 H2 Hummer
Thanks Brendan
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The flashing CEL is the PCM detecting a possible rich mixture that can damage the CAT's
Have you changed any of the rotating assembly like the torque converter or maybe the crank sensor, cam sensor?
You need to look at the long term fuel trims to see if they are more than +/-10%
Typically the PCM will detect a variation in crank acceleration and deceleration from the learned sequence and start flashing the CEL.
The airflow will start high when first cranked up then work its way down once warmed up, usually settle out around 6 to 7 g/s at around 550 rpm

Neal

I have not replaced anything like that, when I start it up cold it's around 10 to 12 gs MAF and after running for about 20 minutes with the engine temp at 1/2 on the gauge it's still the same 10 to 11 gs MAF.

Is there a way to look at long term fuel trim ? Or check the cam crank sensors etc to see if they are bad?

Is it possible to disconnect MAF sensor and run it to see if that is the problem or elimnate that ?

Does the truck feel like its down on power when driving?
You can crank the truck and then unplug the MAF, it will default to open loop. It may stumble when you first unplug the MAF but should run fine.
What is the RPM reading with it idling after warmed up?
You should be able to see the long term fuel trims with the Blue Driver.
If possible have a crank relearn done on your truck, this will reset the top dead center in the PCM, if you can find someone to do it fairly cheap. It requires a scanner with Bi-directional controls. If the crank sensor starts drifting outside of a preset range it can cause the PCM to sense false misfires which will cause the flashing CEL.

Neal

I never drive h2 before but my wife swears it's its gutless om the hi way when gen giving it gas or going ip a hill..
ok how do i check long term fuel trim on blue driver?
if i unplug the Maf what should i be looking for on on the bluedriber ?

I've never used the BlueDriver but have used similar apps, you should have an option to look at all the monitored PID's and within the list should be the long term trims

Need to see what the idle RPM's are to get an idea if the airflow is correct.

Unplugging the MAF really don't tell you much unless there is an issue with it,

Neal

I had this problem with my 05 HUMMER H2 SUT. While I had her in a custom audio shop getting the audio system upgraded, the technician found what was causing the random flashing check engine light issue. Along the frame of the engine, he found a few frayed wires within the wiring harness. He told me can repair the wires for an extra $50. He took pictures and showed me where the frayed wires were at. The technician repaired the frayed wires, reset the ECM, and I didn't have that problem ever since. He you have time, check all wiring. I also had this problem with my 09 H2 SUT as well. My 09-flashing check engine light was more serious, because this would trigger the transmission control module code, in which my H2's transmission would go into limp mode. I just had the all the fluids changed out of my H2 at the proper interval, but I was expecting the worst. I took her to the transmission shop; the technician examines the entire vehicle and found that there's a bad contact within the wiring of the vehicle. Also, there was a service bulletin about certain model year GM trucks and SUVS in which your vehicle may have a flashing check engine light, which may cause your vehicle to go into limp mode. The transmission technician said my transmission for my 09 HUMMER was in very good shape. He cleared all codes associated with the flashing check engine light, and so far, (knock on wood) I haven't has this problem since. I still own my 09 HUMMER H2. I only use it as a weekend driver or for a long road trip.

Did your flashing CEL show up always or just certain times, mine comes when I start driving or rev it up to around 3k ram.

I tried unplugging the MAF when running it sounded like it was going to stall for a split secound but caught itself and kept runningb, ive read that this a good sign of MAF bad BUT some say not always.

So i ran the hummer in the driveway and tried to get a few reading at idle, 1k 2k 3k 4k with the MAF and long tern and short term fuel trims. I thought I saw a video on some kinda math with adding up the fuel trims diving by 2 and comparing to MAF . Any advice on this, I'm thinking of sending the MAF back and try the Delphi one and see if there's a difference..
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all those screen shots look good, MAF readings look steady not jumping around, I don't see an issue with the MAF
When you unplug the MAF it forces the ECM into open loop, it then ignores the MAF sensor and runs on predetermined tables, one down side to doing it is the inlet air temp also resides within the MAF sensor so it will fail the temp to a set temp. The truck should run good enough to drive it and see if the flashing CEL stops
what is the idle rpm once warmed up and in park?
there is a slight difference between the bank 1 and bank 2 long term trims which can indicate there is something wrong. as the rpm rise the difference reduces, this can indicate a vacuum leak on that side.
I would have a crank variation relearn done

Neal

It seems to sit around 850 rpm and the MAF never goes below 10 gs usually 11.5,
it is just rough to start almost like it won't catch then after a while of running it gets better, but can't get away from the flashing CEL and sluggish feel..everything I read or hear says the gs should be about 6 at idle is there a inexpensive bidirectional scan tool for the crank relearn.