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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
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.
The following user(s) said Thank You: jreardon, Pieter
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
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.
The following user(s) said Thank You: jreardon, Pieter
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.
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.
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.
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.
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.
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.
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