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Gents I need some expert opinions! I just had a p0237 code pop up. My truck is running very well and I just averaged 19.7 MPG @70 MPG on the freeway (hand math). Now I have done some preliminary research and I see it’s the map sensor.. I cleared the code and am running the truck. Unfortunately I have an elk hunt that starts Friday and I leave Wednesday morning (not much time for repairs). 

 

What causes the code? Boost leak? Faulty connections?

 

If it comes on again I will be in a different state and it’s up in the mountains do I need to be concerned?

 

As I mentioned above my truck doesn’t seem to be missing a beat but I’ve read the map sensor can effect performance. And if I’m towing a trailer up the AZ grades I don’t want to have issues:duh:

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The fastest, easiest thing you can do is change out the map sensor.  If you don't have time for that then just buy one and put it under the back seat with a wrench to change it if you run into trouble on the road  other wise go through the diagnostics below.

 

 

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1 hour ago, JDHudsn said:

What causes the code? Boost leak? Faulty connections?

 

Most likely the cause. 

  • 5-volt Supply Circuit
  • MAP Signal Circuit Short To Ground
  • MAP Signal Circuit Short To Sensor Ground
  • MAP Sensor
  • Intermittent Wiring Problem

 

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5 hours ago, JDHudsn said:

My truck is running very well and I just averaged 19.7 MPG @70 MPG on the freeway (hand math)

What are you running for timing at that speed, for them tires that's pretty good. 

I would do the ground mod if you haven't already and make sure the alternator is good. 

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11 hours ago, Dieselfuture said:

What are you running for timing at that speed, for them tires that's pretty good. 

I would do the ground mod if you haven't already and make sure the alternator is good. 

I’m running Moparman’s daily tune that he has posted. I was pleasantly surprised because I wasn’t trying to hit high numbers. 

 

Can you also also elaborate on the ground mod? Never heard of that method🤔

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Start by watching boost on the quad at idle, does it read 0?

 

Next week you get on it does boost on the quad increase?

 

 

Does boost increase smoothly or does it jump from 0 to say 16psi?

 

Edited by Me78569

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@Me78569 ima check it in the AM. When I limped home I think it read 0 the entire time on the quad:think:  As I was driving the truck as soon as I shifted to 3rd and got on it it seemed to defuel and not allow any boost to build.  Prior to the limp episode the boost would read 1psi at idle and when you’d let it idle in level 0 it would read 2 psi.. I thought that was always a lil weird. Back when this issue first popped up I bought the replacement MAP on amazon and then I installed it prob mid November. Could this MAP sensor be the culprit?

Edited by JDHudsn

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 I just went thru this a few months back and mine was a wiring issue on the 5v signal wire. Same 237 code with low boost, maybe 50% power, and my Scan Gauge was reading 14.6 on the map. FYI the Scan gauge does not read the map right at all. But my mechanical gauge was showing a little boost and it would build a little as the rpm came up slowly no matter how far you depressed the throttle.

 The weird thing was that it was the 5v to all the other sensors and not the one that goes to the map sensor. Never any code for the other sensors just the MAP. I fixed the wire and mine has run fine since. I have heard here of some folks having trouble with oil pressure sensor going bad and causing issues. It does share a 5v signal wire with the MAP

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Just now, JDHudsn said:

@dripley did you follow an article to fix the 5v wire?

No sir. I have over the past few years dealt with some little gremlins. And during that time it seemed that when ever I went after one another one would go away. Usually after messing with a wiring harness. The last episode was with the MAP sensor. It seemed to go away it I massaged the harness where it comes out of ECM. I do have some splices there after following some bad advice many years ago. I did check those splices, so I thought and they still seemed well connected. What I missed was one more splice buried the harness which happened to be the 5v to the other sensors and it had gotten loose. I fixed it and the problem is gone. Not sure why that did it since the MAP has its own 5v signal. On your 99 the map shares that signal wire with the oil pressure sensor, not so on my 02. My oil pressure switch has no 5v so the map has its own. 

 It is a mystery to me as to why fixing the other 5v stopped my MAP issue. But our symptoms are just about identical. Hopefully someone more electrically inclined can tell us how they are related.

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@dripley electrical demons in the harness are so much fun... haha oh well I guess we can’t expect these dinosaurs to be maintenance free all the time!

I was also wondering if it could be the iQuad pigtail harness that connects to the MAP sensor and another sensor?

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It could be.  
 

test for 5v at the quad main plug,  

 

0 psi at idle tells me that hte ecm is not seeing any boost, so either you have a bad map sensor you have a short in the system.

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Sounds good gents. I’ll be trying to tackle this problem today! I’ll periodically check in and let you guys know what I’m finding. 

 

Thank you!!:thumb1:

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In the FWIW column when mine was doing this I could still drive it, even down the interstate. But acceleration was about 0 to 65 in 2.3 minutes. It always got where I was going. Glad it is fixed though.

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I had a similar issue. No boost, Quad reading zero. Checked voltage on map sensor and was ok. Though I also noticed my oil pressure readings were not what they use to be. Ended up changing both oil pressure sensor and Map sensor and all is well. Kinda wished I did the oil pressure sensor first to see if it was the culprit. It appears both sensors are linked by the 5v supply. 

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ok I have a constant 5v to my map sensor. The oil pressure sensor has always been giving me a good reading. The MAP’s online are $24 but in the parts store they want $120... OUCH

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5 hours ago, JDHudsn said:

@dripley did you follow an article to fix the 5v wire?

Well I just went through this on my 2001.  What I found was that the 5 volt reference voltage connection where it split from the ECM to the Oil pressure gauge and the MAP Sensor had 1,000 ohms resistance.  Should be 0 ohms.  Cut it out and soldered the wires together.  Sealed with Heat shrink tubing and hot glue.

 

Pulled the harness out the bottom in front of the front axle.  Cut it open from there.  Rewrapped with vinyl tape.  4.9 volts at the MAP And the OIL pressure sending unit!!

 

Your 1999 could be different.  My junction was 12-14 in in front (towards the front axle, they bunched the excess wire there) of the ECM junction.

 

Good Luck.

Michael

 

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4 hours ago, Me78569 said:

0 psi at idle tells me that hte ecm is not seeing any boost, so either you have a bad map sensor you have a short in the system

Do have any idea as to why repairing the 5v for the rest sensors made my MAP start working right and other than an odd apps code it thru no other sensor codes? That has always baffled me. I never touched the 5v going to the map sensor.

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they share a 5v source.  I beleive there are 2 5v outputs from the ecm.   

a short in 1 of the sensors can cause issues is the rest of the sensors that share the 5v source.

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Definitely comes off of 2 pins from the ECM. On my 02 the MAP is on its own 5v. Guess I will chalk it up to them there gremlins.

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Ok gents found a map locally got it installed and she is back and very much alive. No more limp mode!! However it still reads 1 psi at idle. Anyone else experiencing that? My factory MAP always read 0 at idle.

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