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I have already tried changing the MAP sensor...no good. I understand that it can be a short to ground, but where in the heck is the wire starting at, and where does it end up....maybe I can cut and run a new wire? I'm trying to ask how to troubleshoot this code and elliminate it. My truck has been showing the SES light for 6 months now with this code, at first it would co9me and go, then shortly there after it was on for good. I have removed all my Banks programming (Big-Hoss and 6-Gun) and cycled the key 6 times, removed the battery terminals for 30 min...and start her up only to find that its not related to the Banks stuff. It has to be a chafed wire some place. Please help!
 

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P0237 - MAP - Turbo boost sensor A circuit low input - Circuit open, short to ground, MAP sensor

The wiring from your MAP sensor goes to the PCM.
The MAP sensor is a 3 wire device with the following circuits

Vref - Circuit 351 Brown/white - You should see 5 V on this with the key on. goes to PCM connector pin 90
MAP Signal - Circuit 358 Lt Green/Black goes to PCM connector pin 79
Signal Return - Circuit 359 Grey/Red goes to PCM connector pin 91

Hope that helps
 

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Going back 9 years in my search for answers to the same question, I stumbled on many similar threads where the final resolution to the original problem is never posted. I hope someone can help:

- SES light out of the blue...

- DTC Code: P0237 (MAP Sensor Signal Return Circuit A low... less than 0.04v)

- Cleared code with NGS, and it immediately reappears in less than a second (25ms polling rate).

- Visually checked wiring, which was protected in doubled up heat resistant protective loom.

- In the 2000, 01, 02, & 03 PCED manuals, PinPoint test DH6 for DTC P0237 calls for less than 5 ohms resistance between the disconnected MAP sensor harness connector at Signal Return Circuit 359 (Gray w/ Red stripe) and ground, with Key ON, engine off. With a Fluke 87, I measured 771,000 ohms to the nearest firewall ground point, and 841,000 ohms directly to the nearest negative battery terminal. :worried:

- HOWEVER, In the 1999 PCED, PinPoint test DH6 calls for less than 5 ohms resistance between the disconnected MAP sensor harness connector at Sig. Ret. Cir. 359 (GY/R) and ground, with Key OFF. I measured 0.8 ohms to the nearest firewall ground point, and 4.5 ohms directly to the nearest negative battery terminal. :spineyes:

- I have a 2000. The 1999 PCED makes more logical sense, due to the results of OTHER TESTS PERFORMED (see below). But since I have a 2000, I don't know what to believe. Some things change, some things stay the same. For example, there was a change between 1995 and 1996 with respect to the MAP signal wiring and the PCM. There was also a change between 1997 and 1999 in MAP signal wiring (moving from PCM pin 34 to pin 79). There was also a major wiring change between 2001 and 2002, but I don't believe that wiring change effected MAP signaling. There is also such a thing as typos. It could be that when the 1999 PCED was updated to 2000, a typo was made and missed, that carried forward to successive years. There is also such a thing as evil. It could be that when Ford was required by the EPA to make PCED manuals open source and free, they put a few puzzles in there to keep the independent shops puzzled and the Ford dealer service departments in business. I know, I'm reaching here, but I am in the puzzled camp right now. The 1999 PCED pinpoint test came from a paid for print, and the other years were checked for free online. Sigh. :dunno:


OTHER TESTS PERFORMED (All PASSED) :

- DH7 Voltage REF Circuit 351 Brown w/White stripe was indeed 5.1 volts. Tested at MAP harness connector (with MAP sensor disconnected)

- DH8 Continuity between Circuit 358 Green w/Black stripe and PCM test Pin 79 was indeed less than 5 ohms... actually 0.6 ohms to be exact. Ford 104 pin breakout box used for this test, with PCM connected.

- DH9 No shorts to ground found between PCM test Pin 79 and case ground, power ground, and all other grounds at PCM pins 25, 51, 76, 77, 91, & 103. Breakout box (BOB) used with PCM disconnected, as instructed.

- With Key ON, Engine OFF, I measured voltage between pins 90 VREF and 91 Signal Return Ground, and found 5.1 volts as expected.

- With PCM disconnected, I measured resistance between Circuit 359 Signal Return and Pin 91, and found 0.1 ohm resistance. To my mind, this means that there is no physical problem with that Gray & Red wire (the one that measured 800,000 ohms in DH6).

And THIS is why I suspect that the PCED for 2000-2003 might be in error for Pinpoint test DH6.

However, I still have DTC P0237, which is what started all this in the first place.

:SM030:
 

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Any chance a range button was accidentally hit while performing first test?
Your second test showed good so I would see what scanner says for reference voltage.Is it showing. 5 ? See what scanner says for battery voltage.No matter what it says on scanner check it at battery.
 

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Actually, the range button was PURPOSELY pressed, after it first came up 0.771 megaohms. The Fluke is auto ranging, but I toggled through all the scales anyway.

After reading your post, I ran back outside and rechecked battery voltage. It was good last night, but hours of the hood being left up, doors open, dozens of Key ON cycles with glow plugs burning and underhood light and cab interior lights burning brought batteries down to 12.07 volts, checked at the batteries. I put them on a small charger now, and they quickly jumped back to 12.45 volts before I headed back in to answer this.

I've got dual alternators, and $460.00 worth of AGM batteries on tap. But my truck is not cocky or anything. :) That was a seriously good call on your part, so thank you, because all this yet to be determined diagnosis time without a recharge of the batteries would likely skew future results, compounding frustration on top of the current frustration.
 

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I have aS ap on Blue point that is a fluke and there is something with the spot they picked for the range button that I am constantly inadvertently hitting it and going oh what the hell.99percent of the time it happens I am doing the funky chicken in the engine compartment of a lifted truck no less.
 

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Ha ha... no accidental meter button presses over here. I'm super careful about that sort of thing, to a fault I think. You probably get more done in a day than I even think about doing for an entire year.
 

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Not sure about that.I am starting to wind down a bit.No more bottom ends.I will do top ends,fuel system and hydro systems.i have two shop I flip any kind of work that will tie me up for any kind of time that is substantial.Some shops will call for diagnostic stumpers,but once I get it their mechanic takes over and I am like wind through the trees with my check.
It is a physically fit young mans game and I am no longer.
 

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UPDATE #1:

Ok, the SES light hasn't returned since I fired it up this morning. That doesn't mean that my problem went away for good. It just means that "the problem could not be duplicated" today. I'll reserve judgment until after a few drive cycles.

Below is my PID report for four stationary rpm levels that I tested a few minutes ago, picked at random off what was saved in the memory of my APCM:

Note 1: The EBP and EBP_V are constantly moving targets within a small amplitude range, so I picked and reported a midpoint within that range for each RPM level.

Note 2: The VREF PID is reported for the exclusive benefit of Nick. :)

Note 3: Inexplicably, the MAP Hertz reported as 0.00 the entire time. This perplexes me, but I'm chalking it up to my misunderstanding maybe. If anyone can shed some light on why the frequency isn't reporting, please do. Since the MAP_HZ values were 0.00 for all RPMs tested, there is no line item for MAP_HZ in the table below.

Note 4: The fact that the MAP has moved from 14.6 at 640 RPM to 16.9 at 2,500 RPM presents another question. Is the increase a calculated value from a look up table in the PCM based on values read from the EBP? Or is the MAP really working. I think it is really working, and actually read the rise in MAP and consequently the related rise in MGP (once MGP rose to a readable resolution of 1 psi increments in the last two columns of higher RPM tests). I have an independent boost gauge tee'd into the MAP hose feed line (all connections confirmed tight), but I amazingly forgot to look for a 1 psi needle bump during the test. Too busy focused on the scan tool readings.



 

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It's probably a modulated pulse being lost in your voltage drop.
The Wgs is duty cycled and they are kinda tied together,the map and wgs that is.
The ebp sensor also works on a 5volt reference signal,just like your map.In fact you can tie a second icp into the pass.head,plug the ebpconnector to the second icp with adapter and watch the difference in pressures via injection and exhaust windows
 

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Ok, I FINALLY edited my earlier post to add the promised spreadsheet of MAP sensor values in the PCM. It took me 45 very painful minutes to do that, but I've always wanted to learn how to present tabular data in an easier to read format, and now seemed to be the time.
 

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It's probably a modulated pulse being lost in your voltage drop.
The Wgs is duty cycled and they are kinda tied together,the map and wgs that is.
The ebp sensor also works on a 5volt reference signal,just like your map.In fact you can tie a second icp into the pass.head,plug the ebpconnector to the second icp with adapter and watch the difference in pressures via injection and exhaust windows

I'm just repeating this back real slow, so as to better understand what and why.
 

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That 5.1 might not be making the journey even though you see it on screen.I don't know if that is actual read voltage or intended.If you unplug icp your screen will immediately say 725.well that's not actual.thats an intended value.Not sure if that the case hereor not.I would turn key on and feel if the waste gate solenoid pulsing.
 

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I don't know how to post video,I just figured out how to rock out while doing this.
Try you tube they have damn near everything.
Somebody has to have videoed two icp's using the ebp sensor connector.
Was just using that as an example of another 5 volt reference item and then interjected the diagnostic tip for those with hydro issues.Didnt mean to get disjointed on ya,sorry.
 

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That 5.1 might not be making the journey even though you see it on screen.I don't know if that is actual read voltage or intended.If you unplug icp your screen will immediately say 725.well that's not actual.thats an intended value.Not sure if that the case hereor not.I would turn key on and feel if the waste gate solenoid pulsing.

If it helps to know, I measured 5.1 VREF with two different instruments:

1. The NGS scan tool, by selecting the VREF PID to constantly run and display with all other PID monitoring.

2. With no scan tool connected, I measured the voltage between pins 90 and 91 on the PCM with a DMM by way of a BOB

Both 1 and 2 reported the same value (5.1). It toggled between 5.00 and 5.1 actually.

I'm aware that the PCM has programming to assume a calculated value in the absence of an actual sensor input in SOME cases, like the MAP sensor for example. But I'm not aware of any PCM programming that assumes, calculates, or fakes a 5 volt reference signal if there isn't sufficient voltage to generate the signal. I'm not ruling ANYTHING out, but that would be news to me.

If a fake 5.1 reference voltage was being calculated or faked, then it seems like so many other operations, sensors, and feedback signals would be effected in some way. Maybe I'm just not understanding what you are saying?

I also want to know what you mean by turning the key and feeling the wastegate solenoid pulsing at the same time. I'd have to have very long arms to do that, unless you are suggesting that the WG is continuously pulsing at idle? The WGC readings on the table above did not behave that way. The WGC was pretty much steady state during any given RPM.

Again, I might be mistranslating what you are trying to tell me. Still listening...
 

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No I understand.i had missed that you physically checked the voltage.I also did not know weather or not that value was a true reading.
I suggested feeling the waste gate solenoid with engine off key on.
My thinking here was that if voltage was being lost it might be lost at the WGS as well.
The waste gate gets juice with key on running or not till the PCM says blow the pressure then the juice is turned off and solenoid allows pressure to pass through to actuator.
With key on engine of you should feel the solenoid pulsing.
I just figured if it was not it might be tied into the MAP circuit problem.
But Nick,my WGS is working ok.ok but that is battery juice and not as susceptible to a voltage drop as a sensor with a five volt reference signal.Now you could have the voltage drop and still feel it pulse if not bad enough but if you have nothing it is probably going to be lost in same are as MAP circuit problem.
My thinking if you found one you might find the other.
 

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Ok, I'm going to go outside and try and "feel" what you are talking about.

(time passes)

Ok, I gave it the ol' boy scout shut my mouth and have faith try... and felt nothing.

I didn't expect to, since the duty cycle is at 0.00% even with the engine running at idle (see table above), never mind with just the key on and the engine off. But I gave it a try, since I don't know what I don't know.

My understanding is that the Wastegate Solenoid that I felt (the little black plastic thingy on the front face of the intake Y spider with the red and green tubes attached) is energized with a PWM circuit commanded by the PCM... and neither the key in run, nor the engine running at idle, meet the conditions where the PCM would send a PWM signal to that solenoid to allow some boost through the red tube to actuate the wastegate.

I didn't go so far as to reach further in to feel the metal wastegate actuator itself, because the electrical PWM signal is not sent to the actuator... which is only activated by a boost (air pressure) input, as enabled by the black plastic wastegate solenoid that does get the electrical signal. I hope that isn't what you meant for me to do and I allowed my own way of thinking to interfere with trying.
 

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Just reviewing your thread, and I'm very surprised that the PCED manuals you checked said to check resistance with the key on. The general rule is NEVER try to read resistance on an energized circuit. :shocked:

I'll have to take a look at my PCED manuals (have a 99, and 01 thru 03 versions) later tonight.

On the Vref, it's generated by the PCM and will likely be rock steady till battery voltage drops below the point where the PCM quits working. That seems to be what I typically see.

I'll check back in on you later.
 

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I was correct in my first explanation of how it works.With the key on with engine running or not that little black waste gate solenoid is energized closing the path to the actuator.when the engine builds the target pressure of boost,the MAP sensor tells the PCM that and the PCM stops energizing and the solenoid relaxes allowing the pressure to pass to the actuator pressurizing it.
I had to double check this myself just the other day when I noticed the solenoid getting audible.
 
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