Another flex fuel enable problem post
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Joined: May 2026
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Another flex fuel enable problem post Hello yall, had another account but ider what the username used to be so new account and here we are....
2003 Silverado 4.8L 4L60e with DBW p59
The OS is 12593058
VCM scanner shows 0% even with 20% ethanol in the tank
I have the "enable" feature turned on with DTCs. I found an old thread referencing using Tuner Cat to enable ff in certain p59s as not all data is there in the OS. That's a bit beyond me though with writing a COS like that...
I also believe segment swapping was another option, but I can't find an OS file with factory FF to use. I've attatched the current bin file below.
Would also like to note I am still using an old laptop with MPVI1 (YES MPVI1 in 2026!). I do have the lastest hpt software installed, but perhaps i need to finally upgrade to the latest mpvi, especially with support ending for the mpvi1 soon here.
2003 Silverado 4.8L 4L60e with DBW p59
The OS is 12593058
VCM scanner shows 0% even with 20% ethanol in the tank
I have the "enable" feature turned on with DTCs. I found an old thread referencing using Tuner Cat to enable ff in certain p59s as not all data is there in the OS. That's a bit beyond me though with writing a COS like that...
I also believe segment swapping was another option, but I can't find an OS file with factory FF to use. I've attatched the current bin file below.
Would also like to note I am still using an old laptop with MPVI1 (YES MPVI1 in 2026!). I do have the lastest hpt software installed, but perhaps i need to finally upgrade to the latest mpvi, especially with support ending for the mpvi1 soon here.
Thread Starter
Registered User
Joined: May 2026
Posts: 2
Likes: 0
I had a friend finally reach out before seeing your response. I attached the file he sent me. Same OS and factory VIN Z.
Doug Deans Base tune 2003 Yukon 5.3 Flex Fuel.hpt
I performed a segment swap and did a write entire. Truck started, runs good, will not enter closed loop. Now I did just have headers installed and such, but i pulled a previous log and found the ltft and stft were adjusting and in CL. In the scanner it looks like my o2 mv is reading, so did i mess up the pcm? I would think they would 0 out or hang at 450mV if an error was present. Would like to additionally note the truck also has a 160* thermostat, but i think my closed loop vs ect is 133* so there shouldn't be a problem from that, especially if only occurring now.
Side not, truck shift hangs. Im assuming i set my rpm and speed scheduling off. probably will revert to factory until this issue is resolved. got too ahead of myself and probably too many changes.
Doug Deans Base tune 2003 Yukon 5.3 Flex Fuel.hpt
I performed a segment swap and did a write entire. Truck started, runs good, will not enter closed loop. Now I did just have headers installed and such, but i pulled a previous log and found the ltft and stft were adjusting and in CL. In the scanner it looks like my o2 mv is reading, so did i mess up the pcm? I would think they would 0 out or hang at 450mV if an error was present. Would like to additionally note the truck also has a 160* thermostat, but i think my closed loop vs ect is 133* so there shouldn't be a problem from that, especially if only occurring now.
Side not, truck shift hangs. Im assuming i set my rpm and speed scheduling off. probably will revert to factory until this issue is resolved. got too ahead of myself and probably too many changes.
