P0129 scare

[Sasquatch]

Got the P0129 atmos. pressure sensor range/perf DTC yesterday, finally got around to looking it up.

The service manual indicates two consecutive 0129 codes replace the ECM to fix.

An ECU reset made it go away. Whew!

[Sasquatch]

Second CEL today. ECU failing? Donkey?

[Ingo]

[QUOTE=Answer
Hi Yusef,
The 0129 means that the voltage shown on the intake manifold's absolute pressure sensor is too low. This might be due either to a problem with the 5v supply wire that operates the sensor or the signal wire which are yellow/pink and violet/brown, respectively, or the sensor itself could have failed. Let me know if you want details as to checking it out with a volt-ohm meter. It may also be the case that one of the vacuum hoses has come loose that is attached to the intake manifold. The symptoms you describe are consistent with this sensor or the intake's vacuum itself being compromised. It should not be a major repair cost problem.
The 016A means that the engine is not responding to your request for power, but it is suggested that any problems with the manifold absolute sensor be corrected first as that may be the cause of this code. If you ask a follow-up question tell me the year and engine size (L). I can send you 6 pages about the measurements to make as an attachment to an email, but I need to know your email address. So if you want those let me know your email address but use the 'private' option in the follow-up question choices.
Roland[/QUOTE]
Above is from a web site "allexperts" on a Crysler 300. Seems it's possibly a vacuum issue, sensor issue or even wiring issue. Hold off replacing the ECU for now...

[Sasquatch]

Thanks for the reference, but the 2004 SOA service manual has this entry in it:

[SD_GR]

I read the table differently. You state it says that after two errors, replace the ECU; however I read it as stating that the CEL will come on after two error cycles, and it only states to replace the ECU if there is another code accompanying the PO129. If there is no other code it is unclear to me what to do.

Have you checked the basic electric connections to the ECU and battery meanwhile?

[Sasquatch]

I agree the manual entry is not exactly clear. No checks of electric connections to the ECU and battery yet. Battery is 2 months old.

[SD_GR]

I'd calmly wait for Donkey because I find it unlikely an 8 year old car will go through not one but two ECUs.

[Donkey]

Did you try a hard reset? The ECU isn't failing per-say. Just the atmospheric sensor inside it is. It's basically a MAP sensor. I'm not really sure how important that sensor is on a modded WRX. It is mainly used for making small atmospheric compensations to the boost tables.


Sent from my magic banana

[Sasquatch]

Hard reset? Disconnect battery for 10+ minutes?

[Donkey]

Hard reset? Disconnect battery for 10+ minutes?

Yup. I generally just disconnect the neg cable and hold the brake pedal down for about a minute,then your good to go.

[Sasquatch]

Yup. I generally just disconnect the neg cable and hold the brake pedal down for about a minute,then your good to go.

Yep, did that over the weekend. Then yesterday's CEL. Was OK today.

I'd calmly wait for Donkey because I find it unlikely an 8 year old car will go through not one but two ECUs.

The original ECU was killed by an v.1 AccessPORT failure during uninstall. I'm no where near panic mode, just looking for the best options at this time. If I have to track down another ECU, so be it.

[SD_GR]

And the main harness to the ECU is secure also?

[Sasquatch]

And the main harness to the ECU is secure also?

I'll check, but I know of no reason it should not be. Was OK today. :shrugs:

[Sasquatch]

More strangeness ...

Now a CEL comes on, but am unable to read anything from the OBDII port. A hard reset makes the CEL go bye-bye and allows reading of the ECU again. This has happened twice.

[SD_GR]

That is odd. I've not heard or seen that before.