Kael

Howdy, got the good old P0300 on my '05 2500 Express when over 50mph. Engine sounds fine as the CEL blinks, so want to try a crank relearn first.
I see various procedures include a scanner to trigger the relearn. Is there an Android app that can do this with a Bluetooth adapter?

If not, what's the "no scanner" method that works? I've noted several variants that are general, not specific.

mountainmanjoe

The first two Google results seem to answer your question
https://sep.yimg.com/ty/cdn/yhst-218...structions.pdf

Why does it need a relearn? Did you change the crankshaft or rebuild the engine?

One of the most common cause of blinking P0300 (constant misfire) is faulty ignition components. If you haven't already, get a fresh set of plug wires. Spark plugs can be inspected visually for the most part (except maybe micro cracks). Coils can be tested with a meter. The entire ignition system can be tested visually also.

What engine do you have?

Kael

Engine is a 4.8L.
The misfire isn't constant, only triggered above 50. And no sign of misfire from my right knee. Drove around town couple of days before, up to 50 sometimes, no CEL.
If it were a plug wire, should indicate a specific cylinder, not just random P0300.
This CEL popped up, same code, before and after I replaced spark plugs. The PO spark plugs were toast, surprised the engine ran at all.

Others have chased the various ignition components and so forth until finally trying a relearn, which fixed the code.
https://chevroletforum.com/forum/exp...000-rpm-86410/

I'm going to get a better scanner than I have now (shows codes only), like my ODBC1. Connect and run an Android app as the interface. Hoped someone knew one that supported relearns and so forth.

Maybe I'll check if local mechanics will do the relearn at non-dealer pricing.

Note the relearn process "without scanner support" relates to specific trucks, meaning the vehicle itself doesn't offer that via a scanner.

mountainmanjoe

a blinking light means persistent misfire (rather than intermittent), or above some threshold.

P0300 can also mean "multiple" misfire, ie more than one cylinder, which wouldn't exclude bad plug wires.

Anyway, I seem to have misunderstood. Are you trying to say that the engine does NOT actually misfire above 50mph. The ONLY symptom is the light. If so then yeah it must be the CKP sensor.

Strange. How would it become unlearned? Or rather why isn't it learning now?

mountainmanjoe

"i went to a performance shop that had a snap on scan tool, 5 minutes and $15."
https://www.gm-trucks.com/forums/top...crank-relearn/

Kael

Yeah, saw that. Now, in Iowa....hmmm.

Kael

Update: Purchased a BAFX EML327 OBD2 scanner interface ( ) and Torque Pro Android app, works great collecting realtime information. Torque Lite is terrible compared to Pro, FYI.

Test drive with data collecting during CLE flash, shows misfires on three cylinders, on the order of 50-60 per second each. Make sense that should sound pretty obvious with the engine cover off?

Torque Pro(TP) collected the code P0300 though the light only flashed for a while, didn't stay. TP said the code indicated "pending misfires" or something, that indicated it was warning there were some misfires but not enough to address immediately.

I really think it's the crank at a certain RPM is the problem. It's a 300,000 mile engine (as far as I know) and probably spinning a little different, due to wear, such that learning is no longer matching.

Checked with one shop so far, they want $130 though they offered to check/replace the crank sensor.

I'm annoyed, this is like my van is running M$ Windows and support wants me to reinstall when I don't have the CD . I'm a Linux person, used to having access to code to figure it out or change if I want to.

mountainmanjoe

yeah vehicle firmware is definitely not open source