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Do I need a new PCM???

 
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  #1 (permalink)  
Old 01 Sep 2015, 07:31 pm
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Join Date: Apr 2013
Posts: 29
Default Do I need a new PCM???

i need some advise. A week ago Sat my check engine light came on (solid not flashing) in my PT Cruiser (2005 turbo convertible, 96000 miles) It has been running beautifully. I took it on Sunday to have the code read. As the technician was scanning it if showed lots of faults but just one code which was that the engine was running too rich (Code 175). He turned off the light and I drove last week (still no performance issues (but it did seem to use a bit more gas than usual) but the check engine light came back on Sunday.


I took it in to mechanic who had it all day and when I called at 4:40 pm he said they were still trying to diagnose the issue. Got a call at 6pm saying I needed a new powertrain control module. Not cheap He said that it is basically the central computer and that when it goes it doesn't communicates with the car So I asked does that mean that it isn;'t actually running rich and he said possibly. I asked if it wasn't communicating with the car why was the car driving so well. He didn't know but he said overtime it can cause problems.

I did a little online research and it sounded like the PCM is often mistakenly identified as the issue when no other obvious cause is apparent
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Old 01 Sep 2015, 07:52 pm
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Join Date: Mar 2012
Location: darien il
Posts: 4,592
Default Re: Do I need a new PCM???

first thing i would do is inspect or replace the air filter.

then i would perform a fuel pressure leak down test. if the injectors are dirty they never fully close and it can make the car run a bit rich. the f.p leakdown test will ID that in a heartbeat. i'd also run some sort of injector cleaner through the car as it's the cheapest/easiest. usually i recommend "berryman's b-12" just because Busted_PT raves about it so much. with it in the tank i recommend beating on the car a bit as in flooring it as much as possible once it's warmed up. when i use it i run it at twice the recommended strength. it's cheap and i actually seem to get better MPG while it's in there.

from there i would test the o2 sensors and their wiring with a multimeter to verify they are in good working order. there is a lot of info about this online, excellent videos on youtube, etc.

if the car has a new air filter, does OK on the fuel pressure leak down test, and the o2's and wiring check out OK, i would then test the MAP sensor with the multimeter.

everything i describe is a bit of labor and learning, but i'd only be spending $3-4 on the cleaner and $7-10 on a basic multimeter. one thing i am uncertain of is how to test the fuel pressure on a 2005 because chrysler in their infinite wisdom eliminated the schrader valve the test gauge attaches to. my car is an earlier model so it still has the test port.

i would be very skeptical of anyone that would throw a PCM at a car just because it is running rich. throwing parts at it is definitely a shadetree and expensive way to fix things....unless you trust the mechanic and feel he has already done all of the above, which i doubt because you're posting about it here.

if the car thinks it's running rich and it is not, it will attempt to correct the issue which can possibly cause it to run lean instead. so you should get to the bottom of it.

if it were my car:
new air filter(or at least make sure it's clean), check the spark plugs
injector cleaner and flooring it from 40-80 a few times once its warmed up
check and clear codes, drive it a week and see if the code comes back. if it does, proceed fuel pressure leakdown test and start testing sensors.

Last edited by rob342; 01 Sep 2015 at 08:06 pm.
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Old 01 Sep 2015, 08:11 pm
Obsessed Cruiser
 
Join Date: Aug 2014
Location: Thousand Oaks, CA
Posts: 7,332
Default Re: Do I need a new PCM???

P0175 Chrysler - Fuel System 2/1 Rich

Possible causes:

Faulty front heated oxygen sensor
Ignition misfiring
Faulty fuel injectors
Exhaust gas leaks
Incorrect fuel pressure
Faulty Mass Air Flow (MAF) sensor

Looks like Rob342 has covered all of the things to check in the previous post!
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Old 01 Sep 2015, 11:34 pm
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Join Date: Dec 2014
Posts: 177
Default Re: Do I need a new PCM???

Quote:
Originally Posted by rob342 View Post
first thing i would do is inspect or replace the air filter.

then i would perform a fuel pressure leak down test. if the injectors are dirty they never fully close and it can make the car run a bit rich. the f.p leakdown test will ID that in a heartbeat. i'd also run some sort of injector cleaner through the car as it's the cheapest/easiest. usually i recommend "berryman's b-12" just because Busted_PT raves about it so much. with it in the tank i recommend beating on the car a bit as in flooring it as much as possible once it's warmed up. when i use it i run it at twice the recommended strength. it's cheap and i actually seem to get better MPG while it's in there.

from there i would test the o2 sensors and their wiring with a multimeter to verify they are in good working order. there is a lot of info about this online, excellent videos on youtube, etc.

if the car has a new air filter, does OK on the fuel pressure leak down test, and the o2's and wiring check out OK, i would then test the MAP sensor with the multimeter.

everything i describe is a bit of labor and learning, but i'd only be spending $3-4 on the cleaner and $7-10 on a basic multimeter. one thing i am uncertain of is how to test the fuel pressure on a 2005 because chrysler in their infinite wisdom eliminated the schrader valve the test gauge attaches to. my car is an earlier model so it still has the test port.

i would be very skeptical of anyone that would throw a PCM at a car just because it is running rich. throwing parts at it is definitely a shadetree and expensive way to fix things....unless you trust the mechanic and feel he has already done all of the above, which i doubt because you're posting about it here.

if the car thinks it's running rich and it is not, it will attempt to correct the issue which can possibly cause it to run lean instead. so you should get to the bottom of it.

if it were my car:
new air filter(or at least make sure it's clean), check the spark plugs
injector cleaner and flooring it from 40-80 a few times once its warmed up
check and clear codes, drive it a week and see if the code comes back. if it does, proceed fuel pressure leakdown test and start testing sensors.
Recently looked into testing the fuel pressure on later models and I guess there's some sort of specialty tool that hooks up in line with your stock fuel lines, disconnect it at the fuel rail and splice in the tool. I can't rember who makes it but I do remember seeing that they may not make it anymore sadly...
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  #5 (permalink)  
Old 02 Sep 2015, 03:32 am
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Join Date: Apr 2013
Posts: 29
Default Re: Do I need a new PCM???

Quote:
Originally Posted by rob342 View Post
first thing i would do is inspect or replace the air filter.

then i would perform a fuel pressure leak down test. if the injectors are dirty they never fully close and it can make the car run a bit rich. the f.p leakdown test will ID that in a heartbeat. i'd also run some sort of injector cleaner through the car as it's the cheapest/easiest. usually i recommend "berryman's b-12" just because Busted_PT raves about it so much. with it in the tank i recommend beating on the car a bit as in flooring it as much as possible once it's warmed up. when i use it i run it at twice the recommended strength. it's cheap and i actually seem to get better MPG while it's in there.

from there i would test the o2 sensors and their wiring with a multimeter to verify they are in good working order. there is a lot of info about this online, excellent videos on youtube, etc.

if the car has a new air filter, does OK on the fuel pressure leak down test, and the o2's and wiring check out OK, i would then test the MAP sensor with the multimeter.

everything i describe is a bit of labor and learning, but i'd only be spending $3-4 on the cleaner and $7-10 on a basic multimeter. one thing i am uncertain of is how to test the fuel pressure on a 2005 because chrysler in their infinite wisdom eliminated the schrader valve the test gauge attaches to. my car is an earlier model so it still has the test port.

i would be very skeptical of anyone that would throw a PCM at a car just because it is running rich. throwing parts at it is definitely a shadetree and expensive way to fix things....unless you trust the mechanic and feel he has already done all of the above, which i doubt because you're posting about it here.

if the car thinks it's running rich and it is not, it will attempt to correct the issue which can possibly cause it to run lean instead. so you should get to the bottom of it.

if it were my car:
new air filter(or at least make sure it's clean), check the spark plugs
injector cleaner and flooring it from 40-80 a few times once its warmed up
check and clear codes, drive it a week and see if the code comes back. if it does, proceed fuel pressure leakdown test and start testing sensors.
Thank you so much for your reply. Very helpful!!
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  #6 (permalink)  
Old 02 Sep 2015, 10:59 am
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Join Date: Apr 2013
Posts: 29
Default Re: Do I need a new PCM???

It turns out this mechanic got a different code. He got PO138 Oxygen Sensor Circuit High Voltage (Bank1, Sensor2), not the PO175 that was read the week before. He said the voltage shoudl be 5 and it was reading .3.
It seems the fix for that is to replace the rear O2 sensor. Does that sound right? Given the PO175 from last week should i consider replacing both O2 sensors?

He did not check the air filter or the fuel preassure, but it sounds like given the reading on the voltage the new O2 sensor may be in order.
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Old 02 Sep 2015, 11:21 am
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Default Re: Do I need a new PCM???

Quote:
Originally Posted by mbelleville View Post
It turns out this mechanic got a different code. He got PO138 Oxygen Sensor Circuit High Voltage (Bank1, Sensor2), not the PO175 that was read the week before. He said the voltage shoudl be 5 and it was reading .3.
It seems the fix for that is to replace the rear O2 sensor. Does that sound right? Given the PO175 from last week should i consider replacing both O2 sensors?

He did not check the air filter or the fuel preassure, but it sounds like given the reading on the voltage the new O2 sensor may be in order.
That's the one on the catalytic converter.
I would just replace the one for now.
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Old 02 Sep 2015, 11:49 am
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Default Re: Do I need a new PCM???

Quote:
Originally Posted by LionPT View Post
That's the one on the catalytic converter.
I would just replace the one for now.
cheap and easy. i'd try it. sure beats a new computer (: if that mechanic is correct and it fixes the problem, i'd say you found a better shop.
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Old 02 Sep 2015, 03:20 pm
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Default Re: Do I need a new PCM???

Quote:
Originally Posted by rob342 View Post
cheap and easy. i'd try it. sure beats a new computer (: if that mechanic is correct and it fixes the problem, i'd say you found a better shop.
Actually the mechanic I spoke with is out of state, a friend of a friend. But the manager of the shop that it is in is discouraging me from just replacing the O2 sensor because he says it isn't going to fix the issue and he doesn't want me to be dissatisifed. He said that it isn't that the whole PCM is necessarily bad but that the driver in the PCM that powers the O2 sensor is and that they can't even test the O2 sensor until they can power it and that it is possible that after they test is I may need a O2 sensor as well.

I said that seems like a pretty expensive approach to replace the whole PCM if just that one specifc driver is bad and can't a PCM be repaired? That prompted him to say the he was going to see if he could find an aftermarket PCM.

I'll probably get a second opinion too. What is strange is the car just passed emmission inspection last month.

I don't even drive this car in the winter so I may just leave it be. What would be the implications if I just don't fix it? He said it wouldn't pass inspection but that's a year away. I read some where that it could danage the cataylitic converter. Is that true?

Last edited by mbelleville; 02 Sep 2015 at 03:26 pm.
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Old 02 Sep 2015, 07:05 pm
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Location: darien il
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Default Re: Do I need a new PCM???

Quote:
Originally Posted by mbelleville View Post
the manager of the shop that it is in is discouraging me from just replacing the O2 sensor because he says it isn't going to fix the issue and he doesn't want me to be dissatisifed. He said that it isn't that the whole PCM is necessarily bad but that the driver in the PCM that powers the O2 sensor is and that they can't even test the O2 sensor until they can power it and that it is possible that after they test is I may need a O2 sensor as well.
that makes perfect sense, and it also implies that he did investigate the wiring as i recommended before telling you what he told you. if he's your normal mechanic and you aren't planning to crawl under the car with a multimeter, i'd take his advice.


Quote:
Originally Posted by mbelleville View Post
I said that seems like a pretty expensive approach to replace the whole PCM if just that one specifc driver is bad and can't a PCM be repaired?
yup. somebody's fixing them. unfortunately a mechanic is not an electrical engineer. then again, neither am I.

repairing my ford ECU: http://www.ptcruiserlinks.com/forum/574128-post218.html

an alien technology embroidery machine: http://www.ptcruiserlinks.com/forum/...tml#post492794

last week it was laptop motherboard: http://www.ptcruiserlinks.com/forum/580110-post278.html

if it were MY pcm, i'd find the wire that is failing to deliver. i'd follow it back into the PCM and look for burned traces, bad capacitors, and any other carnage. maybe i'd fix it, maybe not. unfortunately, you can't expect a "normal" person to do that.

if you DO want the new PCM, there's people on here that have bought them that could offer affordable suggestions.
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