P0108 Code - Keeps Popping Up

[ThorneRock]

I got an interesting code that’s plaguing me.

It’s a P0108-Manifold Absolute Pressure sensor circuit high voltage.

At first, I cleaned the MAP sensor with no change, so I replaced the sensor, and the codes P0108 and P0107 went away.

However, even after replacing the sensor and cleaning all the contacts extremely well, this code still pops after the MAP sensor exceeds its boost rating (36psi) and leaves the P0108 code with the red lightning bolt.

The truck is second gen swapped with S467.7 and 120hp injectors.

Any ideas?


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[AK Bob]

The attached information from Mopar Tech Authority is for my 2014 but may help you troubleshoot.

P0108.pdf


2014 RAM 3500 (Aisin) 3.73 4X4 Limited Crew Cab Long Bed DRW. Oil Bypass Filter, Fuel Filtration Kit and 50 Gallon Aux Fuel Tank.

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[AK Bob]

After reading the theory of operation, l believe your boost mismatch between what the PCM expects to see and the actual boost is causing the trouble code.


2014 RAM 3500 (Aisin) 3.73 4X4 Limited Crew Cab Long Bed DRW. Oil Bypass Filter, Fuel Filtration Kit and 50 Gallon Aux Fuel Tank.

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[ThorneRock]

After reading the theory of operation, l believe your boost mismatch between what the PCM expects to see and the actual boost is causing the trouble code.


2014 RAM 3500 (Aisin) 3.73 4X4 Limited Crew Cab Long Bed DRW. Oil Bypass Filter, Fuel Filtration Kit and 50 Gallon Aux Fuel Tank.

That’s what I was thinking, so the only possible solution would be to have the code tuned out or to upgrade to a higher bar MAP sensor and have the tunes revised for that?


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[ThorneRock]

After reading the theory of operation, l believe your boost mismatch between what the PCM expects to see and actual boost is causing the trouble code.


2014 RAM 3500 (Aisin) 3.73 4X4 Limited Crew Cab Long Bed DRW. Oil Bypass Filter, Fuel Filtration Kit and 50 Gallon Aux Fuel Tank.

Although from what I have seen with others trucks, the MAP sensor just stays tapped out at 36psi but does not show the same code or any code for that matter.


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[AK Bob]

That’s what I was thinking, so the only possible solution would be to have the code tuned out or to upgrade to a higher bar MAP sensor and have the tunes revised for that?

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That sounds about right to me, definitely something to talk to your tuner about.

Hopefully, others will chime in.

Please keep us posted.


2014 RAM 3500 (Aisin) 3.73 4X4 Limited Crew Cab Long Bed DRW. Oil Bypass Filter, Fuel Filtration Kit and 50 Gallon Aux Fuel Tank.

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[AK Bob]

Although from what I have seen with others trucks, the MAP sensor just stays tapped out at 36psi but does not show the same code or any code for that matter.


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Good point, I guess it’s worth troubleshooting the circuit first.

If everything checks out, then talk to your tuner about other options.


2014 RAM 3500 (Aisin) 3.73 4X4 Limited Crew Cab Long Bed DRW. Oil Bypass Filter, Fuel Filtration Kit and 50 Gallon Aux Fuel Tank.

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[Badger2078]

Good point, I guess it’s worth troubleshooting the circuit first.

If everything checks out, then talk to your tuner about other options.


2014 RAM 3500 (Aisin) 3.73 4X4 Limited Crew Cab Long Bed DRW. Oil Bypass Filter, Fuel Filtration Kit and 50 Gallon Aux Fuel Tank.

I agree with you here AK.

I've seen this same code type many times on other vehicles.

Vehicles tend to have a range that is allowed for return on the signal voltage when it comes to 5-volt reference sensors.

If the signal exceeds what the ECM allows it will set a high voltage code.

There are other causes for this code of course but in order to diagnose we generally just hook to a scan tool or use a multimeter to observe the voltage curve.

If the curve is smooth and consistent the sensor is operating properly then it's just a question of whether or not the sensor is on the range and still has the proper resistance of the sensor type can be measured through.

At some point, the sensor is going to return a signal higher than the ECM will accept.

I bet our community dr.

Removes this code from the list on all of our trucks that will exceed 36 psi normally and that's why we don't generally see it.

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[Palladium]

Interesting.

Every once in a while, I throw P0106 - Manifold Absolute Pressure Sensor Performance when I blow past 36lbs of boost. I just normally clear it, and it goes away.

I've never thrown P0108; keep us posted.

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[Muzzy]

I would check the batteries and the charging system.

I started getting various DTCs and the red lightning bolt.

This is a common issue that pops up when your batteries are going bad, or your alternator isn't keeping up.

I swapped two new batteries, checked all connections and ground cables, and solved my problem.

-Muzzy

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