Error codes help please

2003 trailblazer, 166k miles, maintenance good I would say. 4.2 6 cyl. Service engine soon came on day before yesterday. Codes pulled from autozone

Seems to be wheel sensor related, Your input appreciated.

The P0440 could be caused by habitually adding more gas after the pump handle clicks off the first time. If this is the first time you’ve gotten that code, it may clear up in a few days and if you never overfill again, you won’t see it again. It could also be that you didn’t tighten the gas cap enough.

Have you checked the fuses under the hood to make sure they are okay?

I am not in the habit of overfilling, possibly related I do end up running the pump on slow towards the end of a fillup, as otherwise it will burp gas out, and fill the cabin with fumes. Nothing different that way from the last 10 years of experience with the situation.3 days after last fillup when the service engine soon light went on.

Could be a new issue, but blown it off for 8 years, possibility I assume.

@cougar can certainly check the fuses, thanks

An observation . . .

The overwhelming majority of the evap codes I see are NOT caused by overfilling

No offense intended . . . but to me the idea that most evap codes are caused by overfilling and/or a loose gas cap is akin to the idea that most warped rotors and out of round drums are caused by overtightening the lug bolts

That might be somebody else’s opinion, but not mine

I know that nobody here specifically stated that most evap codes are caused by the things mentioned, and I also know nobody here specifically stated that bad rotors/drums are caused by the things I mentioned . . . but the belief persists, in many minds

Like I said, I’m not attacking anybody

I just have an opinion, and experience, which may be polar opposite to somebody else


The codes are C0222, missing RF speed signal, C0226 Missing LF speed signal, C0281 Brake circuit switch fault and C0291, lost communications with the Body Control Module.

Pretty much everything but the rear speed signal has gone down.

Does your ABS work at all? Have you tested it (in a vacant parking lot)? I’d guess the ABS modulator controls have failed. Check the fuse, check the huge connector to the ABS modulator for corrosion and looseness. Failing that, you may need a new ABS unit.

But if the underwhelming minority learn something new and it helps them save money, it’s not bad advice.

No abs light, I had to renew my license plates today, luckily not an emission testing year. All the C codes do not play into the emission test so only the po440 code important now. Purge valve or gas cap 2 most common issues for that code. Thanks for the ideas!

Tapping your experience re p0440 error code,evap system problem. Cleaned mating surfaces of gas cap and filler neck today, and noticed the little flap in the filler hole is not closing flush. I am thinking it might be an issue, anyone know is the metal tab a potential issue?

That little tab inside the filler tube is part of the emissions evap control system, so the fact that it isn’t working correctly is definitely a possibility as the cause of the evap code. Me, I’d start by getting that fixed first. It might well solve the evap code problem completely.

Gas cap: On my Corolla there’s an o-ring that sometimes failes to seal air tight, and it gets flagged during emissions testing. I’m always able to get it sealing enough to pass the test by wiping it clean with a tissue, then rubbing a tiny amount of motor oil on the o-ring surface.

The two things you mention are the most likely causes. Next in line is the canister and the various tubing that connect all the evap stuff together. For the canister to work correctly it has to be able to allow air into the canister to replace the gasoline purged from it. And visa versa. If that mechanism gets clogged up, that could be a cause.

C-codes: Work on them by starting on the lower numbered ones first. Sometimes once you fix that problem, the higher number ones will fix themselves.

Thanks @GeorgeSanJose for the info.

P0440, Evaporative emission control system malfunction is set if a negative pressure was not seen during a self test. Usually a large leak causes this but this code is used when it is uncertain if there is a leak.

For example if the vent solenoid fails to close during the monitor test there will be no measured vacuum but there is no system leak.

Check the integrity of everything, the cap, the purge line to the engine, the purge valve operation (it should not draw vacuum with the wiring disconnected).

Try disconnecting the Speed sensor at the wheel and see if there is any corrosion on either side of the connection. Maybe a little cleaning might restore the wheel speed signals. It worked for me on our 2003 minivan. We did have an ABS light, and this took care of it. Maybe a little wire brushing on the electrical contacts is all it needs.

I got a new gas cap yesterday, and today the warning light turned off. YeeHa. A mechanic at the dealer said the flapper being out of place wont affect anything, in fact in 2006 they stopped putting them in that model. So just a little more character for the old car.

No warning lights so I’ll get to the other codes later.