DTC P0107 MAP Sensor (ALH engine)

[AndyBees]

I recently did a lot of work to the ALH engine and associated things in my 84 Vanagon. In fact, I started working on in on June 3, 2024 and did not move it out of the garage until September 12th.

Anyway, I replaced the wires (cable with 9 wires) that go from the rear to the front. I replaced it with a 15 wire cable but only used 6 of those wires. I added 3 separate wires which are larger (16 gauge) vs the 22 gauge in the 15 wire cable. These 9 circuits involve the brake and clutch pedal switches. I need them to kick-out the cruise and satisfy the ECU with respect to a brake light.

None of the above pertains to the circuits for the MAP Sensor. The circuits to the MAP sensor have never been cut. They go directly to the ECU (no connectors, OE or otherwise). I did relocate the MAP sensor from the side of the Intercooler to the down stream pipe on the Intercooler.

The scan says P0107, intermittent low voltage. I did install a brand new Bosch MAP sensor which did not change the DTC. I did the engine install in 2010-12. I've never had this DTC to appear previously. I do not see relocating the MAP sensor to be related to low voltage. The connector looks just fine. Doing the work, I did not unplug the ECU. It is located under the back seat, thus, no water there.

The engine starts fine. It has accelerator response, but no boost due to the MAP sensor issue, I assume. Before I did the work, the engine would almost immediately go into limp mode. The DTCs related to the Accelerator Pedal and Brake Switch, if I remember correctly. I believe the bad wire(s) in the 9 wire cable to be the culprit. Which, again, shouldn't have anything to do with the MAP sensor.

Thoughts?

 

[P2B]

According to Ross Tech that code can pertain to the MAP or the barometric pressure sensor inside the ECU.

What does VCDS have to say about the readings from these two sensors? Do they match with key on/engine off?

Have you verified the MAP sensor has power (5v)? The MAP also contains the IAT sensor, is that reading correctly?

 

[AndyBees]

Yeah, I was through and through the wiring harness, sensors, etc., when I did the engine conversion. I am aware of the components in the MAP sensor. But, I had forgot about the barometric pressure sensor being inside the ECU.

Although I have driven the Van almost 20 miles after moving it out of the garage about 10 days ago, when I posted last evening, was the first time I'd done the scan, jotted down the code and looked it up aside from what VCDS was saying. Remember, this is a conversion. So, I cannot save codes because I have no VIN for it. There are only two things I can scan, Engine and the Gateway.

So, today, I did check voltage. Unfortunately, neither the sensor or the connector has the the four circuits labeled (i.e., 1 2 3 4). So, unless there is only one of the four wires with voltage, yes, there is 5 volts on one circuit. Looking at the connector with the release/slot at the top, the 2nd circuit from the left has 5+ volts on it.

I did install another ECU which doesn't have the Immoblizer disabled. It will allow the engine to start but it shuts down immediately as it suppose to do. I get the same volt readings with it at the MAP connector.

I guess the question now, do those two sensors (MAP & IAT) operate off the same voltage source (that single circuit with 5 volts)?

Anyway, it would seem the voltage comes from the ECU via it's 12 volt source(s). However, I did unplug and inspect all the fuses. Everything seemed okay. Of the circuits I have plug/connectors as part of the conversion, I unplugged and reconnected them. No change.

Thoughts?

 

[P2B]

MAP pin 2 is reference voltage, so that seems right. Also check you have a good ground on pin 1. The IAT is probably a thermistor, in which case it would need ground but not the 5v reference.

Did you check the sensor readings as I suggested? Measuring block 10 has MAP and barometric I believe.

 

[oilhammer]

MAP and IAT share the same ground I believe, the brown w/ blue wire (not a solid brown, because it is a switched ground through the ECU?)

The IAT is just a resistance to that ground, based on temperature, the MAP is a conventional 3-wire arrangement... 5v reference, a ground, signal back to ECU.

VAG has a bad habit of not labelling the 5v reference circuits, and even though in this case that wire (along with the rest) from the MAP/IAT go directly to the ECU, they will be internally bussed with some other 5v circuit to some other sensor(s).

I only say that because you mentioned some pedal position sensors. There might be a shared 5v reference with one of those. Usually, the dual pedal position sensors (they do that for safety/redundancy) are NOT on the same 5v circuit.

 

[AndyBees]

Guys, thanks for the input. It is very much appreciated.

This is my situation. The Van is no longer inside the garage. It started raining here around 2:30 pm. So, I quit fiddling with it.
I made my way to the garage where I commenced working on my formerly owned 2000 Jetta with 400k miles on it. In another thread, I asked if the axle flange seals could be changed without removing the transmission. All the parts come today. When the rain hit, it was time to dig-in with the Jetta.

So, I did get the axles and flange stubs out. It will need new ball joints which are among the parts I ordered.

My son uses the Jetta for his relay vehicle. He's an engineer for CSX Railroad. So, he needs two vehicles. He don't like my ol' 89 Vanagon ...LOL

Also, I have a dental appoint tomorrow, a dermatologist appointment Wednesday and a local water district board meeting Thursday (I'm a member.) And, seems there is a volunteer fire department board meeting Thursday evening. Thus, I plan to use all available time to finish up the Jetta.

So, it may be Friday before I can get serious with the TDI Van again. But, I will take time to look at the MAP info with VCDS.

 

[AndyBees]

With the OE ECU plugged up, these are the numbers with the engine idling!

Group 10: Barometric Pressure is 969 and Actual 969
Group 11: Demand is 999 and Actual 969.

Maybe sometime later this week or the weekend, I'll find the time to ohms test each circuit back to the ECU connectors.

 

[P2B]

Those are sensible numbers and the two sensors agree, so the fault must be intermittent.

 

[AndyBees]

Yeah, VCDS says it is intermittent. However, the 15 or so miles I drove it on the back roads in my neck of the woods there was zero boost. My Boost Gauge stayed on zero or a little below during acceleration which was obviously extremely sluggish on the level.

 

[P2B]

It wouldn't surprise me if the ECU decided that DTC warrants limp mode, and if the fault was detected at key on limp mode would be permanent.

 

[AndyBees]

Well, as I stated in my initial post, since early June until early September, I did a lot of work to the Van. The primary reason was Limp Mode. The engine would default to 1200 RPMs. The problem was associated with the brake and clutch circuits which are only needed in the conversion to make the Cruise Control safe and keep the ECU happy so there'd be no CEL relating to them. Keep in mind, I did install the Jetta Cluster in place of the Vanagon Cluster. So, about all the bells & whistles that can come on or alert you, will, if something is amiss.

That Limp Mode could be corrected by a re-start which generally took care of it for a good number of miles. Sometimes it would come back when I touched the brake pedal. Sometimes it would immediately go into Limp Mode upon starting the engine. Part of the work I recently did, involved replacing the cable that contained those wires. That issue is gone (no fast idle and no CEL relating to the brake or clutch switches).

So, did I cause a bad connection somewhere while working on the Vanagon back in the summer? According to the Bentley, there are no connections between the MAP sensor and wires through and to the ECU plug/connector. Maybe I need to check to see if a mouse has chewed on the wires. When I drove it to my work garage back in June, if I remember correctly, the CEL was on. I cannot remember if the GP light was flashing. And, I do not remember the specific DTCs when it was going into Limp Mode previously.

Well, like I said, I need to do an ohms test on the four circuits between the ECU and the MAP sensor.

 

[AndyBees]

Okay, the rain stopped for most of the afternoon. So, here is what I found doing Ohms readings on the individual 4 Circuits.

First off, the circuits are numbered on the Connector at the MAP Sensor. When you pull back the rubber seal on the Connector, the numbers are quite visible. Left to right looking face on at the end of the Connector - 1 - 2 - 3 - 4

G72 is the Intake Air Temp sensor

#1- Brown/Blue: goes to 121/52 on the ECU Connector. It has an Ohms reading of 1.7 to 1.9 (sort of up and down)
#2- Gray/Green: goes to 121/73 on the ECU Connector. It has an Ohms reading of 0.138 and fairly steady right there
Number 2 is the circuit that has 5 volts on it.

G71 is Manifold Absolute Pressure sensor

#3- Lilac/Red: goes to 121/31 on the ECU Connector. It has an Ohms reading of "nothing" (no matter what I did, no movement at all)
#4- Yellow/Black: Goes to 121/71 on the ECU Connector. It has an Ohms reading of 0.321 and fairly steady right there

Inspection of the wiring loom under the back seat where the ECU is located looked good without any doubt.

As I was looking at the bundle of wires (4-wires) going to the MAP sensor connector which is inside a convoluted wire loom, it dawned on me that most likely I spliced the wires in order to reach the area of the MAP sensor on the Inter Cooler.

So, I need to slide those wires out of the convoluted loom for an inspection.

I'll report back with the results, most likely, Monday afternoon.

 

[AndyBees]

Update.

Well, as I posted above in the last two or three sentences, yes, I did cut the wires to lengthen them.

As I remember, early in my conversion project, I was soldiering splices. Someone commented that soldered splices could cause a problem with connectivity. So, I began twisting splices covered with shrink tubing.

Anyway, this afternoon I had an opportunity to look into the continuity issue of these circuits. The previous post shows the ohms readings and one had nothing. Well, today, I got zero on all four circuits.

So, I broke down the splices closest to the connector at the MAP sensor. From there, I checked each circuit. I still have one that is not showing anything. I suppose the next step is to find the splices on the other side.

 

[KLXD]

Soldering causing connectivity problems??? Wow! How?

I can see not soldering causing causing connectivity today, none tomorrow.

Some might argue a properly done crimp is superior to solder. I don't like the major stress concentration and the corrosion point of the typical Autozone connectors unless they're covered with heat shrink that melts inside instead of the insulator they come with. And how many people buy the ratcheting crimper to make sure it's done right?

I solder and use the "adhesive" lined shrink sleeve.

Sorry this is no help on your problem.

 

[AndyBees]

Soldering causing connectivity problems??? Wow! How?

I can see not soldering causing causing connectivity today, none tomorrow.

Some might argue a properly done crimp is superior to solder. I don't like the major stress concentration and the corrosion point of the typical Autozone connectors unless they're covered with heat shrink that melts inside instead of the insulator they come with. And how many people buy the ratcheting crimper to make sure it's done right?

I solder and use the "adhesive" lined shrink sleeve.

Sorry this is no help on your problem.

Yep! I learned the hard way. I had actually gone back and disassembled all the twisted splices and solder them and used the adhesive shrink sleeves like you. But, obviously, I forgot about the four circuits to the MAP sensor. Butt crimps are okay for larger wires used on brakes, etc., I suppose ...LOL

The #3 wire splice toward the middle of the run looked perfect but the ohms meter would not register anything. It had the adhesive lined shrink sleeve. It looked just fine. There was no corrosion on or about the splice. Strange to say the least. Amazingly, I had driven this conversion project just shine of 90k miles over about 10 years with zero electrical issues.

Anyway, this afternoon, I stripped the four wires out and disassembled the splices and solder and slide the sleeves over then used the heat gun. Now, no DTC for the MAP. But, that darn brake pedal circuit is still acting up. Also, seems there is a vacuum leak because my dash mounted vacuum gauge will not get above 18 inches and the brakes will go hard with two pumps. Obviously, the Turbo function is affected.

More work to do on this contraption.

EDIT: Ironically, solder "connects" 99% of everything inside the ECU ........ there! Proof solder is not a connectivity issue with these things!

 

[starrd]

Sounds like you corrected the issue. Thought I would share what I found after chasing a map sensor issue forever on my son's 2003 Golf ALH. He was getting the following codes at different times

00575 - Intake Manifold Pressure
17-10 - Control Difference - Intermittent

17964 - Charge Pressure Control
P1556 - 35-10 - Negative Deviation - Intermittent

16490 - Manifold / Barometric Pressure Sensor (G71) / (F96)
P0106 - 35 - 00 - Implausible Signal

When his car went into limp mode, a key cycle would correct the issue. I finally got pissed off and ran 2 new wires between the map sensor and the ECU plug. I did this with MAP pin 3 (5vdc supply - purple/red to ECU pin 31 ) and pin 4 (pressure signal voltage - yellow/black to ECU pin 71) only because the ground is common with the IAT sensor and it never showed it was an issue.

While doing this, I was acquainted with the ECU pin connectors and how they connect to the wires (insulation-displacement)- see below

When I de-pinned the 2 wires, it seemed that one of the connectors wasn't fully seated so the connecter was recessed in the plug. I am not sure if this was the issue, but after replacing the 2 wires there has not been a re-occurrence of any codes for months now. I plan on putting the original wires back into service one at a time and hopefully get the 2 external wires removed.

My point to all of this is:
1) ohm testing the 2 wires generally showed a good connection, but a long time ago, I could get the resistance to vary if I twisted the ECU cable bundle
2) understand that the ECU pin connectors are an insulation displacement connector - could be an issue
3) if the connector is not properly seated (holding tab not engaged) in the ECU connector, that can also cause issues because it does not seat properly with the pin at the ECU (I'm pretty sure this was our problem)

 

[oilhammer]

Soldering is for component internals, connections are crimped. VAG has a pretty good method on this, and there was an article years ago in Import Service (a magazine... before the internet) that did a pretty extensive test and concluded the Germans were right.

But, it does require the proper parts and tools and methods.

Lots of modern components don't even get internally soldered connections anymore. Just push pins.

 

[AndyBees]

Starrd, thanks for sharing your experience with the connectors. My ECU is located under the back seat of the Van. So, it is out of the weather. But, the Intercooler and MAP sensor are located behind the left rear wheel, with some protection. I did move MAP location up and behind the left rear tail light assembly. So, it is now out of the weather much better.

Oilhammer, that surprises me about the internal connections of an ECU. I've only opened one. I did it on the spot in a Junk Yard pick. The wiring loom had been removed. I wanted to see if it had water damage inside. It looked perfect. But, my inspection was just a glance. It looked so perfect that I just assumed those components were soldered in place. Thanks for that tidbit of info.

Well, I've neglected my TDI Vanagon due to these issues. It sit parked for several months. So, as I may have already posted, I started working on in the first week of June. It sit in my garage all summer. I worked on it as I could .......... intake off, turbo off (gaskets leaking), transmission out, stripped out 9 bad wires relating to the brake switch function for cruise cut-out, dash out due to grounding issues, fuel tank out to repair the level sensor unit, radiator out, new AC Compressor, new starter, new alternator, Timing Belt Job, etc.

I've not got over that darn 2nd COVID vaccine. It and COVID six months later in January, 2022, left me with very low energy. So, my work days are short.