Misfire While In Tow/haul Mode

chas0218 · May 31, 2011

This weekend was the first time I had to use tow/haul mode. When I was driving down the highway my check engine light came on and start flashing at me. My fiancee pulled the owners manual out and it said if the check engine light flashes there was a misfire. The light stayed on solid for ~9 miles then turned off. I used the mode again and same thing happened. The third time no light. This kind of has me puzzled. The light has been off and has not come back on for 100+ miles.

Has anyone else ran into this issue and did you have to fix anything?

This is all on a 03 5.3L.

Thanks,

Chas

hrspwr · May 31, 2011

Was tow/haul mode being used when you were pulling something?

The more load that the engine is under, the better chance that a misfire will happen with a bad component (wire, coil, etc). When you were driving and the light did not come on, did you ever put the truck under a load, accelerate quick/hard?

cujo8 · May 31, 2011

This weekend was the first time I had to use tow/haul mode. When I was driving down the highway my check engine light came on and start flashing at me. My fiancee pulled the owners manual out and it said if the check engine light flashes there was a misfire. The light stayed on solid for ~9 miles then turned off. I used the mode again and same thing happened. The third time no light. This kind of has me puzzled. The light has been off and has not come back on for 100+ miles.

Has anyone else ran into this issue and did you have to fix anything?

This is all on a 03 5.3L.

Thanks,

Chas

I had this happen with my 2006 GMC 5.3L truck in which I installed a Black Bear tuned computer. I had this happen multiple times when I was hauling a fully loaded (firewood) 6'x16' Utility trailer while in Tow-Haul mode. It never did this when the trailer was empty, but only when loaded. I reinstalled my stock computer and I had no problem towing a similar size load of firewood. I then reinstalled the BB tuned computer and the same problem came back when I tried to haul another load of firewood. The BB tuned computer was great when I was not towing, but misfired while towing heavy loads. BTW, I had Justin leave the Tow-Haul mode in its stock configuration, since I planned to use my truck for occasional towing needs. I never figured out why the BB tuned computer had issues when towing, I would just installed my stock computer when I needed to tow. I would suggest you get the dealer to reflash your computer modules to see if this cures this issue, since for me it was computer related. Hope this helps.

chas0218 · May 31, 2011

Was tow/haul mode being used when you were pulling something?
The more load that the engine is under, the better chance that a misfire will happen with a bad component (wire, coil, etc). When you were driving and the light did not come on, did you ever put the truck under a load, accelerate quick/hard?

No I was accelerating slower than I usually do just because I had a load. I had about 1100lbs. give or take a few loaded in the bed. Once it was unloaded and tow/haul mode was off there wasn't any light. The last time I used the tow/haul mode the light never came back on.

I had this happen with my 2006 GMC 5.3L truck in which I installed a Black Bear tuned computer. I had this happen multiple times when I was hauling a fully loaded (firewood) 6'x16' Utility trailer while in Tow-Haul mode. It never did this when the trailer was empty, but only when loaded. I reinstalled my stock computer and I had no problem towing a similar size load of firewood. I then reinstalled the BB tuned computer and the same problem came back when I tried to haul another load of firewood. The BB tuned computer was great when I was not towing, but misfired while towing heavy loads. BTW, I had Justin leave the Tow-Haul mode in its stock configuration, since I planned to use my truck for occasional towing needs. I never figured out why the BB tuned computer had issues when towing, I would just installed my stock computer when I needed to tow. I would suggest you get the dealer to reflash your computer modules to see if this cures this issue, since for me it was computer related. Hope this helps.

The truck and computer is all stock and I was thinking about having my computer updated (I don't think it has ever been done) because of my 1st to 2nd flare shift and now because of this.

I have never had the misfire code before while driving it in the normal mode.