Anyone got any insight on PCM replacement on GM's? ('01 Cavalier)

[phucheneh]

edit: this is old, just posted update at bottom in case anyone gives a shit.

Okay, so I'm working on a 2001 Cavalier with the old 2.2L. CEL on, P0440. Like most evap codes, it's a 'something is wrong with me but I don't know what' code.

I'll try and add in a little education here while also describing what I'm running into. If no one can help, hell, maybe I'll at least help someone else.

When the evap monitor (self-test) runs on most vehicles: the normally-closed purge valve opens. Vapors are pulled by engine vacuum through the system and into the engine. Then the normally-open canister valve closes (allowing vacuum to be pulled on the evap system). Then the purge valve closes, and a pressure sensor monitors the system to check for malfunctions.

P0440 means either the requisite vacuum was never pulled on the evap system, or that said vacuum went away too quickly. Possible causes: bad canister valve or wiring, a leak in the system, bad purge valve or wiring, saturated charcoal canister (has liquid fuel in it)...that's about it, as far as I can think right now.

There's another code for no flow through the purge valve, much like there is for the EGR system. But, as far as I can tell, this vehicle is not set up to monitor that. You could also have a vacuum leak on the engine intake side of the valve causing the leak, but this would generally set other DTC's or at least give some very telling data (fuel trim issues).

I spent hours going through this damn car. I know the canister valve seals. I know it has power. I don't have the equipment to manually trigger it through the ECM, so I do need to do one more test concerning the ground wire to make sure the wiring is okay (ECM turns it on by grounding it). But I'm 99% sure it will pass this test, as I've found a different issue.

No leaks. Certain of this. And I've pulled the hose off the charcoal canister to check for fuel (comes from 'topping off' the tank and flooding it).

So okay, I tell the owner. It has to be the purge valve or its wiring. I need to remove the upper intake stuff to be able to easily get to it and check the wiring, so that's what I do.

Key on, engine off, connector unplugged, I've got 12v on one side of the valve. Test light confirms that this hot wire can carry a load (no high resistance fault due to damaged wiring).

Then it gets weird. I've got ground on the other side. The PCM is not supposed to open the purge on engine start, so this is a problem.

But what happens when I plug in the valve? Nothing. Plug in a new valve? Nothing. Checked ground with a test light...this wire will NOT carry a load. There is far too much resistance between it and true battery ground. Confirmed by manually grounding this connection and listening to the valve click.

Unwanted ground goes away when the key is turned off. Starting to suspect the driver for this circuit inside the PCM is bad.

Unplug PCM, and check continuity between every single terminal of the connectors and this fuckin' wonky ground wire at the purge valve. Only one terminal has continuity, which means, ideally, there is no short to ground in the engine harness. The design of the connector, and fact that it is undamaged, makes me extremely dubious of a short through the connector, and I can manually trace the wire in question back to the stationary part of the engine harness.

Conclusion: PCM, you be fucking broken. As one last test, I plug the PCM back up, and backprobe the ground (control) wire for the purge valve at the PCM. I do the 'load test' again- hook test light ground up to my probe, positive right to the battery. Nothing.

So the PCM is grounding the valve when it shouldn't, AND it's a half-assed, barely there ground (explaining why the engine does not have a vacuum leak through the purge valve- can't open). But wait! I grab my DMM again, and check for ground on this wire at the PCM...nope, nothing. Move back up to the connection at the valve...nope, no ground there either.

I'm thinking...hoping...that disconnecting the PCM from its power source has temporarily unfucked things. Once it tries to open the purge valve again, the half-assed stuck-on ground circuit will probably return.

So I need to replace the PCM. Go figure, an important computer being mounted in the front bumper is having problems.

I know when I need to transport my laptop, I always am sure to strap it beneath my car. Foolproof, right?

Blargh...the actual questions are coming...

 

[phucheneh]

The question: how cheaply can I get this done for this person? I am, unsurprisingly, not a GM guy. I've been trying to google up the damn answer, but I've been unsuccessful. I see PLENTY of used (and new) PCM's for sale, but I can't find anything that mentions if simply replacing it will actually work.

On most modern cars (with CAN bus, especially), most ECU's...that's electronic control unit; something with an integrated circuit (processor) in it that controls something. Could be the engine, could be a power window...anyway, most ECU's need programming. Some new parts don't even come with software on them. Used parts, you often have to program with the vehicle info and VIN so that it will 'sync' with the rest of the system.

I just don't know if that's the case here. So all this long-winded, fairly technical shit...is to ask one simple question, really:

What's the plug-and-play ability on this vehicle, or on this era of GM in general? Can I plug in a different 2.2L, AT Cavalier PCM and have everything work? Or is the car gonna tell me to go fuck myself?

 

[BUTCH1]

Cliffs, please..

 

[phucheneh]

Cliffs, please..

second post.

 

[bruceb]

You need the correct one for that year and model and then it may need to be flashed with the proper software (which is on the GM site by VIN number) You may not be able to do this yourself, as that is sometimes restricted to dealers and authorized service centers and you will need a GM Tech II tool to do it.

 

[Bartman39]

^...ditto...:thumbsup:

It will have to be flashed the vin code will not match and the most it will do is crank run for 1-2 seconds (maybe) and die or not run at all...

Unwanted ground goes away when the key is turned off. Starting to suspect the driver for this circuit inside the PCM is bad.

Very common...

 

[BUTCH1]

You need the correct one for that year and model and then it may need to be flashed with the proper software (which is on the GM site by VIN number) You may not be able to do this yourself, as that is sometimes restricted to dealers and authorized service centers and you will need a GM Tech II tool to do it.

Yup, my '05 Chevy needed a BCM flash for a starting issue, dealer had a satellite linkup direct to GM to do it. In the early days of computer controlled cars you could go to the bone-yard and plug and play a control module but sadly, not anymore..

 

[BUTCH1]

OP, if your feeling brave and can solder maybe it's possible to replace the transistor or op-amp that's driving the solenoid, it should be heat-sunk somehow so you might be able to spot it, since the PCM won't function as is not much to lose. Also check the electrolytic caps (if any) they never age well, even good quality ones..

 

[SpatiallyAware]

Advance has these for $200 and doesn't say anything about requiring programming by the dealer..

 

[phucheneh]

Advance has these for $200 and doesn't say anything about requiring programming by the dealer..

1) That is unbelievably cheap. Which is cool. But...

2) http://shop.advanceautoparts.com/we...-cardone_10150154-p?searchTerm=pcm#fragment-2

If that doesn't go to thr right part, hit the 'specs' tab

Flash Programming Required: Yes

Shittles. Who would have thought Advance Auto would have useful information?

I knew this car was right on the edge...I know I had a suspected PCM issue with Jetta only two years older (...turns out to be wires rubbing together...I was not quite so thorough then...) and I was able to just stab one in from a parts car. I don't even think it was the same year...no issues.

 

[phucheneh]

OP, if your feeling brave and can solder maybe it's possible to replace the transistor or op-amp that's driving the solenoid, it should be heat-sunk somehow so you might be able to spot it, since the PCM won't function as is not much to lose. Also check the electrolytic caps (if any) they never age well, even good quality ones..

The problem here is that the car runs and drives...just throws an evap code. I don't want to have to save, 'welp, now it doesn't, because I accidentally totally fuckin' smoked your PCM...'

edit: also thanks for the replies, guys, I didn't know if anyone would be able to endure my rambling. But I figured if GM was still having PCM issues around ~2000, someone had probably run into it. Personally, I thought by then that 'the computer did it (in the library with the candlestick!)' was usually grasping at straws...They just don't fail on newer cars like they used to on early computer-controlled engines (80's, early 90's, mostly).

But again, the placement of this thing just seems absolutely retarded, and this is an Illinois car...

 

[bruceb]

Have a look at this link: http://www.obd-codes.com/p0440

 

[SyndromeOCZ]

I generally get my Dodge PCM's off of ebay for 100-200$. I do have to send them my vin and my mileage so they can flash it, but I've gotten a few of them and they have all worked perfectly. After doing the pcm in my brothers mini van it went from 16mpg to 20mpg.

 

[BUTCH1]

Have a look at this link: http://www.obd-codes.com/p0440

Nice, thanks, might come in handy, bookedmarked..

 

[BUTCH1]

The problem here is that the car runs and drives...just throws an evap code. I don't want to have to save, 'welp, now it doesn't, because I accidentally totally fuckin' smoked your PCM...'

edit: also thanks for the replies, guys, I didn't know if anyone would be able to endure my rambling. But I figured if GM was still having PCM issues around ~2000, someone had probably run into it. Personally, I thought by then that 'the computer did it (in the library with the candlestick!)' was usually grasping at straws...They just don't fail on newer cars like they used to on early computer-controlled engines (80's, early 90's, mostly).

But again, the placement of this thing just seems absolutely retarded, and this is an Illinois car...

From what I've heard the BCM fail is common on later GM's, an ex co-worker used to maintain a fleet that had a lot of Impalas, he said it was common. The car might run in "limp" or open loop (not using the O2 sensors) while the code is present..

 

[1prophet]

Instead of wasting your time (unless your time is of no value) go to

http://www.acdelcotechconnect.com/html/tss_tech_esi.jsp



and you can access all the factory information for 3 days for the price of one Andrew Jackson plus tax.

 

[phucheneh]

Instead of wasting your time (unless your time is of no value) go to

http://www.acdelcotechconnect.com/html/tss_tech_esi.jsp



and you can access all the factory information for 3 days for the price of one Andrew Jackson plus tax.

Which would've helped me how, now? The biggest help would've been a wiring diagram...and I ultimately really didn't have too much need for that.

Is it that I might need the trouble trees most manufacturers now want their low-paid, inept, borderline retarded techs to use? Nah, I'm good there. And I don't have factory test equipment (scan tool for activating solenoids, mostly), which would render their methodology moot.

Also I try not to give money to GM if I can help it. 3 day access? Nice to see they're getting their business models from porn sites. Except with the patented GM bloat added in.

Everyone else, thanks for the info. I'll just have to see if one of the local dealers will do the likely ~5 minutes of labor needed for the programming for a reasonable rate.

 

[1prophet]

Which would've helped me how, now? The biggest help would've been a wiring diagram...and I ultimately really didn't have too much need for that.

Is it that I might need the trouble trees most manufacturers now want their low-paid, inept, borderline retarded techs to use? Nah, I'm good there. And I don't have factory test equipment (scan tool for activating solenoids, mostly), which would render their methodology moot.

Also I try not to give money to GM if I can help it. 3 day access? Nice to see they're getting their business models from porn sites. Except with the patented GM bloat added in.

Everyone else, thanks for the info. I'll just have to see if one of the local dealers will do the likely ~5 minutes of labor needed for the programming for a reasonable rate.

Maybe not for you now but it might help someone who doesn't want to spend hours and possible needless parts replacement which definitely exceeds 20 dollars.

 

[5150MyU]

DESCRIPTION P0440
The EVAP large leak test applies vacuum to the Evaporative Emission (EVAP) system and monitors vacuum decay. The Powertrain Control Module (PCM) monitors the Fuel Tank Pressure (FTP) sensor signal to determine the vacuum decay rate. At an appropriate time, the PCM turns the EVAP canister purge valve ON (open) and the EVAP vent valve ON (closed). This allows the engine to draw a vacuum on the EVAP system. At a calibrated time, or vacuum level, the PCM turns the purge valve OFF (closed), sealing the system, and monitors the FTP sensor input in order to determine EVAP system vacuum. If the system is unable to achieve the calibrated vacuum level, or the vacuum level decreases too rapidly, DTC P0440 will set.
CONDITIONS FOR RUNNING THE DTC

DTCs P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0452, or P0453 are not set.
The ignition voltage is between 10-18 volts .
The Barometric Pressure (BARO) is more than 75 kPa .
The fuel level is between 15-85 percent .
The Engine Coolant Temperature (ECT) is between 4-30°C (39-86°F) .
The Intake Air Temperature (IAT) is between4-30°C (39-86°F) .
The start up ECT and IAT are within 9°C (16°F) of each other.
The Vehicle Speed Sensor (VSS) is less than 121 km/h (75 mph) .
CONDITIONS FOR SETTING THE DTC
The EVAP System is not able to achieve or maintain vacuum during the diagnostic test.
ACTION TAKEN WHEN THE DTC SETS

The control module illuminates the Malfunction Indicator Lamp (MIL) when the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.
CONDITIONS FOR CLEARING THE MIL/DTC

The control module turns OFF the Malfunction Indicator Lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Use a scan tool in order to clear the MIL and the DTC.
DIAGNOSTIC AIDS

Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to set occurs. This may assist in diagnosing the condition.
Use the EVAP Pressure/Purge Diagnostic Station in order to pressurize the EVAP system to aid in locating intermittent leaks. Move all EVAP components while testing with the Ultrasonic Leak Detector.
A temporary blockage in the EVAP canister purge valve, purge pipe or EVAP canister could cause an intermittent condition. To repair a blockage in the EVAP system refer to Evaporative Emission (EVAP) System Cleaning. See: Powertrain Management\Emission Control Systems\Evaporative Emissions System\Service and Repair

 

[5150MyU]

ok

 

[5150MyU]

ok

 

[5150MyU]

ok

 

[5150MyU]

ok

 

[5150MyU]

Sorry but I had to delete the diagnostic trouble tree.I can repost them if you need them I just have to change the file names.

 

[phucheneh]

DESCRIPTION P0440
The EVAP large leak test applies vacuum to the Evaporative Emission (EVAP) system and monitors vacuum decay. The Powertrain Control Module (PCM) monitors the Fuel Tank Pressure (FTP) sensor signal to determine the vacuum decay rate. At an appropriate time, the PCM turns the EVAP canister purge valve ON (open) and the EVAP vent valve ON (closed). This allows the engine to draw a vacuum on the EVAP system. At a calibrated time, or vacuum level, the PCM turns the purge valve OFF (closed), sealing the system, and monitors the FTP sensor input in order to determine EVAP system vacuum. If the system is unable to achieve the calibrated vacuum level, or the vacuum level decreases too rapidly, DTC P0440 will set.
CONDITIONS FOR RUNNING THE DTC

DTCs P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0452, or P0453 are not set.
The ignition voltage is between 10-18 volts .
The Barometric Pressure (BARO) is more than 75 kPa .
The fuel level is between 15-85 percent .
The Engine Coolant Temperature (ECT) is between 4-30°C (39-86°F) .
The Intake Air Temperature (IAT) is between4-30°C (39-86°F) .
The start up ECT and IAT are within 9°C (16°F) of each other.
The Vehicle Speed Sensor (VSS) is less than 121 km/h (75 mph) .
CONDITIONS FOR SETTING THE DTC
The EVAP System is not able to achieve or maintain vacuum during the diagnostic test.
ACTION TAKEN WHEN THE DTC SETS

The control module illuminates the Malfunction Indicator Lamp (MIL) when the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.
CONDITIONS FOR CLEARING THE MIL/DTC

The control module turns OFF the Malfunction Indicator Lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Use a scan tool in order to clear the MIL and the DTC.
DIAGNOSTIC AIDS

Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to set occurs. This may assist in diagnosing the condition.
Use the EVAP Pressure/Purge Diagnostic Station in order to pressurize the EVAP system to aid in locating intermittent leaks. Move all EVAP components while testing with the Ultrasonic Leak Detector.
A temporary blockage in the EVAP canister purge valve, purge pipe or EVAP canister could cause an intermittent condition. To repair a blockage in the EVAP system refer to Evaporative Emission (EVAP) System Cleaning. See: Powertrain Management\Emission Control Systems\Evaporative Emissions System\Service and Repair

Is this GM's info? It pretty much agrees with everything I know regarding this code and generic OBD2 (I explained the requirements for it setting in less detail in the OP).

I know some manufacturers are much more associated with certain codes, even from the same problem. That's why evap stuff can suck if you're not working at the dealership and specializing in one make (or an independent that maybe does a few; e.g. we have some 'euro' shops that are mostly BMW/Mercedes, maybe a little VW/Audi). Heck, one make's 'gas cap' code- as in, what sets due to a very loose, missing, or cross-threaded cap (yep, seen people manage to do that...usually Mazdas...have to use channel locks to remove it)....it can be different for another. Usually it's P0455, but I've also seen P0456...I remember Toyotas like to set P0442 as well..it's kind of a crap shoot.

But anyway, I try to assume the code actually fits its generic definition and work from there. The manufacturer info is appreciated; however, as I already stated rather plainly (and not nicely), I despise trouble trees. They're a dumbing down of my occupation, and worse than that, they're often wrong or not informative enough...i.e. telling you to check 'x' wire for 'y' voltage or resistance, without giving complete information...you may not know where the connector they're talking about is, or whether it's disconnected/which side they're probing from. Or maybe there's no pinout (on a, say, 20 pin connector without markings, 'pin 3' could mean at least four different things).

'Wrong' is when a trouble tree tells you something is fine because there's no resistance on a circuit with no load...that's terribly wrong info, as one tiny strand of wire touching at an otherwise broken connection can lead to a 0ohm reading on a DMM (they pass very little current to get their readings...no real 'load'). Among other examples.

If you're lucky, the info that you need is present elsewhere (wiring diagrams, pinouts, connector locations, signal specs), and that's where I've learned to look- not at the 'hey I have code Pxxxx what do I do now' section of the service manual.

When I'm working with NO info (e.g. everything I do now), I'm simply learned to compensate. My methodology described in the first post, imo, is pretty good, if not a bit convoluted...PCM replacement isn't a conclusion I jump to easily. Had I had a GM Tech II or better (surely they've moved on to PC based?), I could've tried to activate the purge solenoid manually and immediately found the 'source' of the code...but I would've been wrong as to knowing what part was actually needed unless I went more in-depth.

Anyway, point being- as I said when I posted, I went in-detail for a couple reasons: one, to maybe help those who have trouble with general diagnostic method a little bit (or maybe even some random googler who's having the exact same problem as me). Two, so that anyone who cared to read could point out any possible flaw in my logic that I may have missed. Not really looking for diag advice, otherwise. Just wanted to know if anyone had seen similar issues out of the that vintage of GM PCM, and if anyone knew what had to be done to replace them.

If you wanna REALLY help me out, look up PCM replacement- or 'ECM,' I can't remember what term GM likes to use; I say 'PCM' since many people confuse 'ECM' and 'ECU' (engine control module, as opposed to the more generalized 'electronic control module' or 'electronic control unit').

But anyhow, yeah, if you can cut/paste the replacement procedure for the PCM (i.e. describe the requisite reprogramming procedure), I would definitely appreciate that.