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Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!

Dodge Ram 5.7 2008 erratic idling

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4 years 5 months ago #48777 by Pieter
Dodge Ram 5.7 2008 erratic idling was created by Pieter
Hi. I have a Dodge Ram with idling problem. Sometimes it idles and then just wants to die unless you rev it up. With the ignition on and map sensor unplugged I get 5v on 1 pin and 4.9v on other pin. I measured-12v on middle pin. With ignition on in live data I see barometric pressure at 102 kPa but map vacuum only at 0.98 kPa. It has a fault p0108 map sensor circuit low. P0129 barometric pressure out of range low. Anybody that can help me identify if it is a faulty map sensor as I expect the map vacuum with ignition on to be the same as baro.
Thanks Pieter

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4 years 5 months ago - 4 years 5 months ago #48780 by jreardon
Replied by jreardon on topic Dodge Ram 5.7 2008 erratic idling
Double check that negative 12 volts. That's a sensor ground from PCM, zero volts.

500
Last edit: 4 years 5 months ago by jreardon.
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4 years 5 months ago #48781 by Pieter
Replied by Pieter on topic Dodge Ram 5.7 2008 erratic idling
If I measure battery negative to Dark blue its 0 volts.

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4 years 5 months ago #48782 by Heon
Replied by Heon on topic Dodge Ram 5.7 2008 erratic idling
That sounds better. Now that barometric pressure reading looks about right. 101.9 kPa is 30 inches of mercury (just type into google "101.9 kPa in inHg" and you get instant conversion). I think your MAP sensor's not malfunctioning, at least not right now. I'm not totally sure about this but I don't think the MAP vacuum PID will update if the engine's off.
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4 years 5 months ago #48784 by jreardon
Replied by jreardon on topic Dodge Ram 5.7 2008 erratic idling
Anything in Freeze Frame data,? I wonder what voltage it detected on the signal wire to set that code
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4 years 5 months ago #48789 by Pieter
Replied by Pieter on topic Dodge Ram 5.7 2008 erratic idling
I dont have any freeze frame as faults have been cleared. I am taking it for a drive every now and then to see if I can get the fault back again. Thanks for the help so far. This is not a common vehicle in my country. It has been converted from Lhd to Rhd

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4 years 5 months ago #48791 by Matt T
Replied by Matt T on topic Dodge Ram 5.7 2008 erratic idling
That BARO might be a substituted value. Personally I'd verify the 5V ref and sensor ground are good with a test light then jump the signal to sensor ground with the light and see if the MAP voltage PID gets pulled to 0V.
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4 years 5 months ago #48792 by Pieter
Replied by Pieter on topic Dodge Ram 5.7 2008 erratic idling
I will try that in the morning when I am back at the shop. Thanks for the advice. Can I just use a wire to jump between the 2 pins.

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4 years 5 months ago #48793 by Pieter
Replied by Pieter on topic Dodge Ram 5.7 2008 erratic idling
Ok I see you said I must use the light to bridge. Will do

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4 years 5 months ago #48794 by Pieter
Replied by Pieter on topic Dodge Ram 5.7 2008 erratic idling
I went back to the shop as this thing is bugging me. I tested the 5v ref circuit with test light and went on dim. I tested between the sensor ground and the signal wire and on the live data it went from 5v to 0v.

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4 years 5 months ago #48795 by Matt T
Replied by Matt T on topic Dodge Ram 5.7 2008 erratic idling

Pieter wrote: I went back to the shop as this thing is bugging me. I tested the 5v ref circuit with test light and went on dim. I tested between the sensor ground and the signal wire and on the live data it went from 5v to 0v.


Wiring is good. Sounds like MAP is bad. Wouldn't hurt to start the truck just to see if the MAP pressure and voltage PIDs change though.
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4 years 5 months ago #48797 by Pieter
Replied by Pieter on topic Dodge Ram 5.7 2008 erratic idling
I checked the sensor using scope if that is any help. It's just a photo and not a screenshot.

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4 years 5 months ago #48799 by jreardon
Replied by jreardon on topic Dodge Ram 5.7 2008 erratic idling
Do the female terminals look okay? With your eye on scope, very gently flex the connector and see if the signal voltage jumps to 5v (open circuit voltage) or flatlines to 0v (short to ground/shorted sensor). Give it some taps with your finger. Turn the wheel, rock the truck, brake torque it, go through the gears, do you have a hair drier

To address the concern if the map sensor is causing the erratic idle I'd simulate a map failure by jumping the signal wire to ground and quite simply unplugging the connector to simulate an open circuit in signal wire.

I've attached the DTC flowchart to help others follow along in thread.

File Attachment:

File Name: p0108.pdf
File Size:287 KB

File Attachment:

File Name: p0129.pdf
File Size:325 KB
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4 years 5 months ago #48800 by Matt T
Replied by Matt T on topic Dodge Ram 5.7 2008 erratic idling

jreardon wrote: I've attached the DTC flowchart to help others follow along in thread.


Seems odd that one code is high voltage and the other is low voltage. I'm wondering if at least one of them has been set by testing???
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4 years 5 months ago #48801 by Matt T
Replied by Matt T on topic Dodge Ram 5.7 2008 erratic idling

Pieter wrote: I checked the sensor using scope if that is any help. It's just a photo and not a screenshot


Seems to be responding. What was the engine doing when that capture was taken?

Also I'm wondering whether your Autel is misreporting MAP pressure? Do you have another scan tool you could get a second opinion with? Or you could get out of O.E. and try generic with the Autel.
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4 years 5 months ago #48805 by Pieter
Replied by Pieter on topic Dodge Ram 5.7 2008 erratic idling
I will give that a shot and see how truck responds when doing it. I have a heat gun so i will set it on low and warm it up abit. Thanks

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4 years 5 months ago - 4 years 5 months ago #48806 by Pieter
Replied by Pieter on topic Dodge Ram 5.7 2008 erratic idling
When i did the test with scope it was idling for an instance. I went into special functions and selected the option for idle speed and it gives different rpm ranges. When i choose 1 then it is usually about a 100 rpm below the desired rpm but when it is set at a certain rpm in that mode it will stay idling and not cut out. I also have this I took with the autel and I also found this in 1 of the connections in the room. Looks like water got into the connector. Had little bit of corrosion.
Last edit: 4 years 5 months ago by Pieter.

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4 years 5 months ago - 4 years 5 months ago #48889 by Pieter
Replied by Pieter on topic Dodge Ram 5.7 2008 erratic idling
Just an update. Did all the tests and ended with it pointing towards a ecu problem. Checked wiring and got another map sensor from other jeep that came in and still the same. Customer coming to fetch the vehicle. So no definitive end result. Thanks for all the help. Greatly appreciated.
Last edit: 4 years 5 months ago by Pieter.

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