The Chrysler Minivan Fan Club Forums banner

1 - 20 of 21 Posts

·
Registered
Joined
·
378 Posts
Discussion Starter #1
I have both of these codes, indicating a problem with the heating circuit of the oxygen sensors. I changed the post cat sensor, because it was also throwing other codes and the pre cat sensor, because it was old. After I cleared the codes, the other ones stayed off, but P0135 & P0141 came back. Is it likely a PCM issue? If it was just one sensor, I'd think it was a wiring issue, but with both that seems unlikely to me.

Thanks,
 

·
Registered
Joined
·
1,122 Posts
The O2 sensor heater circuits share the same ground, so that would be one suspect. Check the black wire(s) on pin #1 to see if there's good solid ground.
 

·
Registered
Joined
·
378 Posts
Discussion Starter #4
I checked the voltage between pins 1 and 2 with the car in the start position and got 1.15 volts. I also checked between pin 2 and the negative terminal of the battery, just to rule out a ground problem. It also came up 1.15. I'm assuming it should be 12 volts.
 

·
Registered
Joined
·
1,122 Posts
I checked the voltage between pins 1 and 2 with the car in the start position and got 1.15 volts. ....
Was it running or at least cranking? If not, then the ASD relay does not get energized, and B+ voltage isn't sent to pin #2.

I'm wondering if perhaps those O2 sensor codes are being retained by the PCM. I know that a 2004 is quite a bit earlier than when the permanent emissions DTCs were implemented around 2010, but perhaps this is something that Chrysler started doing before the official stuff arrived later on.

Anyway, you can test that theory out by disconnecting the battery overnight, in order to completely clear computer learned memory, and take it back to the factory settings. If those O2 sensor codes come back after the battery disconnect, then it's back to square 1 for more testing.
 

·
Registered
Joined
·
2,555 Posts
OP, first PCM's are very reliable, more likely wiring than anything else.

Also, if your state doesn't have emissions testing, the heater ckt just stays on for a few seconds when the car is started to improve cold O2 sensor performance. You can choose to ignore, and you'll be fine.
 

·
Registered
Joined
·
378 Posts
Discussion Starter #7
Thanks for the additional suggestions. The car runs fine, but unfortunately, I live in a state with emissions testing. The ground seems good, so if it's a wiring problem, it has to be in the "heater control" wires coming from the PCM. They are separate wires that follow mostly different paths for both sensors (the upstream wire goes to a harness in front of the engine, the rear one goes on the side of the engine, where it's more likely to have issues, because of heat). That's why I thought it was unlikely that it's a wiring problem.

I have cleared the codes multiple times and they always come back. I tried disconnecting the battery for a couple hours once to totally reset things and that didn't help either.

The sensors I bought were Denso and NTK, so I don't think it's a sensor issue. I may try buying a single Mopar sensor and see if that helps and then buy the other one, if it does. I think that my only getting 1.15 volts between pin 1 and 2 means it isn't a sensor issue, though.
 

·
Registered
Joined
·
378 Posts
Discussion Starter #8
Was it running or at least cranking? If not, then the ASD relay does not get energized, and B+ voltage isn't sent to pin #2.

I'm wondering if perhaps those O2 sensor codes are being retained by the PCM. I know that a 2004 is quite a bit earlier than when the permanent emissions DTCs were implemented around 2010, but perhaps this is something that Chrysler started doing before the official stuff arrived later on.

Anyway, you can test that theory out by disconnecting the battery overnight, in order to completely clear computer learned memory, and take it back to the factory settings. If those O2 sensor codes come back after the battery disconnect, then it's back to square 1 for more testing.
I just checked the voltage with the car running. I get 9 volts.
 

·
Registered
Joined
·
1,122 Posts
I just checked the voltage with the car running. I get 9 volts.
Ok, that's interesting because 9V would not be as quick to heat as 12V, and so it fits in with what the codes are saying about the O2 sensor heater not coming up to temp fast enough. But the missing link here is that the FSM doesn't specify the voltage test that you just did in the flowchart for those codes. They use the DRBIII tool for part of the testing, and a resistance test for the rest of it. I would think that seeing only 9V on the heater wire indicates a problem, but can't say that's true for certain.

Before getting into possibly measuring resistance from the connector back to the PCM, can you also measure the other O2 pin #2 voltage right after a cold start? Yes I know it's a bit of a PITA, but at this point it's starting to look like a PCM problem, because the O2 sensor heater wires come directly from the PCM without getting routed through the IPM, which means that the only other remaining suspect would be those wires/connectors. So you would like to have all of the other related test information before resorting to a replacement PCM.
 

·
Registered
Joined
·
378 Posts
Discussion Starter #10
Ok, that's interesting because 9V would not be as quick to heat as 12V, and so it fits in with what the codes are saying about the O2 sensor heater not coming up to temp fast enough. But the missing link here is that the FSM doesn't specify the voltage test that you just did in the flowchart for those codes. They use the DRBIII tool for part of the testing, and a resistance test for the rest of it. I would think that seeing only 9V on the heater wire indicates a problem, but can't say that's true for certain.

Before getting into possibly measuring resistance from the connector back to the PCM, can you also measure the other O2 pin #2 voltage right after a cold start? Yes I know it's a bit of a PITA, but at this point it's starting to look like a PCM problem, because the O2 sensor heater wires come directly from the PCM without getting routed through the IPM, which means that the only other remaining suspect would be those wires/connectors. So you would like to have all of the other related test information before resorting to a replacement PCM.
I just checked the post cat heater O2 sensor's pin 2 voltage. It was only 6.85 volts. The pre cat 02 sensor's pin 2 voltage was 9.4 volts. I'm thinking the next step may be to check the voltage of the wires going to pin 2 of the sensors close to the PCM. Also, I wonder if there's corrosion on the connector attaching to the PCM. Do you know which connector it is (I think they're color coded, if I remember correctly) and what color wires I should be looking for?

Thanks so much for your continued help.
 

·
Registered
Joined
·
1,122 Posts
.... I'm thinking the next step may be to check the voltage of the wires going to pin 2 of the sensors close to the PCM. ...
That would be difficult, although it probably could be done with wire-piercing multi-meter adapters. The standard way to check that section of the circuits is to measure the resistance between the #2 O2 sensor wires and the corresponding wire at the PCM connector. Around 1/2 ohm is the specified max acceptable resistance.

The upstream O2 #2 wire is located at connector 2 (C2), pin # 18 at the PCM.
The downstream O2 #2 wire is located at C3, pin # 9 at the PCM. All you need to do is test the resistance between those connector endpoints.

... Also, I wonder if there's corrosion on the connector attaching to the PCM. ....
Interesting you mentioning that, because I'm fairly certain it happened on my '05. Last year the radiator fans were not running, and previous testing had taken me all the way back to the PCM. The final test was to ground the specific control pin at the PCM connector, in order to see if that would spin the fans. It did, which 'confirmed' a bad PCM. I didn't have a replacement PCM at that point, so I reconnected everything and ordered a new computer. Well, lo and behold, I discovered that the fans were working again, before the new PCM arrived!

Curiously, the pins of the PCM connectors did not appear to have any corrosion on them, but aside from that the only other possibility was some internal circuit issue (soldering, ....), which was 'fixed' by unplugging and reinstalling the connector. I believe corrosion on the connector pins is by far the most likely suspect of those two possibilities.

So I can say it's a definite possibility, however in the case of your van, the issue is happening from wiring in 2 separate PCM connectors powering different sensors. If you can actually see corrosion, then the likelihood goes up considerably. But in any case it's probably worth a shot to reconnect everything and try one more time to see if either or both codes are eliminated, before considering a replacement PCM.
 

·
Registered
Joined
·
378 Posts
Discussion Starter #12
That would be difficult, although it probably could be done with wire-piercing multi-meter adapters. The standard way to check that section of the circuits is to measure the resistance between the #2 O2 sensor wires and the corresponding wire at the PCM connector. Around 1/2 ohm is the specified max acceptable resistance.

The upstream O2 #2 wire is located at connector 2 (C2), pin # 18 at the PCM.
The downstream O2 #2 wire is located at C3, pin # 9 at the PCM. All you need to do is test the resistance between those connector endpoints.
Thanks. I didn't realize they are on separate connectors. That does seem to make the chance that it's corrosion pretty small. I will check the resistance later today or tomorrow. At this point, it seems that it's very likely to be the PCM.
 

·
Registered
Joined
·
1,122 Posts
... At this point, it seems that it's very likely to be the PCM.
Once the resistance of the heater wires/connectors is (likely) confirmed to be good; there's one more thing you could try that would basically 100% confirm the PCM isn't sending the correct heater circuit voltage, and causing the codes to be set.

That test would be to cut the upstream O2 sensor harness #2 wire, and splice in a temporary fused jumper from that wire to the B+ battery post. But you probably wouldn't want to cut the new sensor harness and then have to solder/tape it back up later, so do you still have the old sensor to run that test with? If you can run that test, and if the P0135 code disappears, it becomes a virtual certainty that the PCM needs to be replaced (again assuming that the resistance back up to the PCM has been confirmed good).
 

·
Registered
Joined
·
378 Posts
Discussion Starter #15
Once the resistance of the heater wires/connectors is (likely) confirmed to be good; there's one more thing you could try that would basically 100% confirm the PCM isn't sending the correct heater circuit voltage, and causing the codes to be set.

That test would be to cut the upstream O2 sensor harness #2 wire, and splice in a temporary fused jumper from that wire to the B+ battery post. But you probably wouldn't want to cut the new sensor harness and then have to solder/tape it back up later, so do you still have the old sensor to run that test with? If you can run that test, and if the P0135 code disappears, it becomes a virtual certainty that the PCM needs to be replaced (again assuming that the resistance back up to the PCM has been confirmed good).
I get almost no resistance from pin 2 of the O2 connector to the PCM connector (my meter reads almost the same resistance as when I touch both probes together) so the wiring is good. There was no corrosion visible on the connectors at all. I didn't try connecting power directly to pin 2, because I didn't have time. At this point, it seems that the problem has to be the PCM.
 

·
Registered
Joined
·
1,122 Posts
....At this point, it seems that the problem has to be the PCM.
Seems to be coming down to that. Did you also check the static and running voltage at the battery? Our vans can be fussy about that, and you wouldn't want to hang on a PCM, only to find out that the codes are the result of a charging system issue.
 

·
Registered
Joined
·
378 Posts
Discussion Starter #17
Seems to be coming down to that. Did you also check the static and running voltage at the battery? Our vans can be fussy about that, and you wouldn't want to hang on a PCM, only to find out that the codes are the result of a charging system issue.
Yes, I forgot to mention that I checked that first. Both running and static voltages were good. I think the static voltage was 12.65 and running voltage was 14.4.
 

·
Registered
Joined
·
1,122 Posts
Although the computer is normally last on my list of possible suspects, in this case it appears to be the cause of your van's issues. The only other possibility I can think of is the IPM messing up and sending bad voltage to the PCM. However, I'd expect the PCM to test the input voltage and set a code if it's not good.
 

·
Registered
Joined
·
378 Posts
Discussion Starter #19
Although the computer is normally last on my list of possible suspects, in this case it appears to be the cause of your van's issues. The only other possibility I can think of is the IPM messing up and sending bad voltage to the PCM. However, I'd expect the PCM to test the input voltage and set a code if it's not good.
Even though it seems like it has to be the PCM, I'm not all that confident that replacing it will solve the problem. It seems like if it was the IPM, that even if the PCM didn't check for low input voltage that all sorts of other things would be malfunctioning too. I'll post an update after I replace the PCM.
 

·
Registered
Joined
·
378 Posts
Discussion Starter #20
I put a remanufactured PCM in yesterday and it fixed the problem! It's super easy to change, except that one bolt broke, even though I sprayed PB Blaster on them the day before I did it. I just put one bolt on each side. I bought the PCM on eBay for $133 and even though it said it was going to be a remanufactured unit, I thought it would just be a reprogrammed used one, because it was so cheap. Of course, I can't see inside of it, but from the outside it looks very good. Thanks for all the help, cvguy.


IMG_4221.JPG
IMG_4220.JPG
 
1 - 20 of 21 Posts
Top