SES light on and no codes

[a5150nut]

Ok first problem with this truck for me. 2006 K3500 D/A 56k miles. Got an SES light, (no limp mode) just before getting home from a two week trip with fifth wheel.

Checked for codes and there are none. Checked under hood for low levels on fluids, loose wires, anything obvious and turned up nothing. Oil change is 75% and fuel filter is fresh 12/17/15.

Other than a better scanner, what will set SES light and not leave a code?

[DmaxMaverick]

If it's a tranny or body code, your scanner may not be able to see it. Tranny codes will usually set a P0700, which is the DTC that triggers the MIL/SES lamp when the tranny has a complaint. Nearly any basic reader should be able to read the P0700 (but not the issue-specific DTC), so your problem isn't likely an issue with the tranny.

[a5150nut]

If it's a tranny or body code, your scanner may not be able to see it. Tranny codes will usually set a P0700, which is the DTC that triggers the MIL/SES lamp when the tranny has a complaint. Nearly any basic reader should be able to read the P0700 (but not the issue-specific DTC), so your problem isn't likely an issue with the tranny.

Thank you for that. Allison's aren't cheep.

Is there a pedal KOKO procedure on these to clear codes?

[DmaxMaverick]

Nope. No KOKO. That went by the wayside in 1995.

You can clear them, and reset the PCM to default:
Disconnect BOTH batt+ cables and ground one (discharges static and residual power). Wait at least 30 minutes (longer, such as overnight, is OK). UNGROUND BOTH batt+ cables and reconnect them. Wait about 2 minutes before KO or starting. If it doesn't work, repeat with a longer ground period. Most of them reset in 15-20 minutes, but some take a little longer. I don't know of one that's taken longer than 30 minutes, but I haven't done them all. Overnight never failed, though. That's also a good time to service, de-sulfate and trickle up the batteries, while disconnected (unless they're relatively new, of course).

[a5150nut]

Well today I had to go help my brother move so I filled the tank. And Pooof! SES is gone. Don't know if it was filing her up or key cycles that did it but SES is gone.

Now it will bug the shi!! out of me not knowing what caused it. You know Murphy, he will pop his head up at the most inopportune time. . . . . .

[DmaxMaverick]

Sometimes, things just happen with no explanation. I have one recurring code that comes and goes, but it's somewhat predictable. I don't recall the DTC, but it's for a fuel temp error, accompanied with an unlisted (for the model year) "U" code, and it only happens during fall and spring, when the overnight temp and startup temp is specific. The fuel code sets the SES, but the "U" code alone doesn't. It's relatively harmless, and I'll do nothing about it. The only issue it causes is, sometimes it will cause the gear ratio program adjustment (for larger tires) to revert. It goes unnoticed until I get up to speed and the TC locks, when the tach doesn't match the speedo where it should. It takes about a minute to reprogram that, so no biggie. The codes disappear at the next startup once up to operating temp, and don't remain in history.

If the SES goes away and causes nothing negative, I'd just move on and not look back. If it returns, maybe have another look. Or not.