# Sensor Reference Circuit "B" open circuit, DTC for CPS, and wonky MAP readings?



## punkassjim (Sep 22, 2002)

Hey y'all, I'm a bit rusty with the troubleshooting skills, so I need some fresh eyeballs on this:

*The source of the problem:*
A body shop did a terrible job repairing the front end of my '09 Jetta 2.5, so the radiator and fans started tipping backward, and the fan mangled the wiring bundle that runs over top of the throttle body.

I unwrapped the bundle, clipped out the mangled bits of the affected wires, and spliced/soldered patches before taping up the bundle again. The major wires that were damaged were one fat ground wire, and all three wires in a twisted triplet that goes to the Camshaft Position Sensor (G40). One of the wires to that sensor also shares the circuit with the MAP sensor and Secondary Air Inection sensor. I tested my wire repairs with a multimeter, they are solid.

*The Problem:*
The vehicle is stuck in limp mode, no power past 3k rpm. The ECU is throwing two codes:

001617 - Sensor Reference Voltage B, P0651 - 000 - Open Circuit - MIL ON
000835 - Camshaft Position Sensor (G40), P0343 - 000 - Signal too High - MIL ON
Using VCDS, measuring blocks shows a consistent 100.0 mBar from the MAP sensor, regardless whether the car is running, under load, or turned off completely. That's a problem, and it's surprising that there's no DTC being thrown for bad MAP.

I've replaced the Camshaft Position Sensor (DTC persists), and the MAP Sensor (100 mBar persists). I find it strange that the "Reference Circuit B: open circuit" code is still being thrown, since I did a really solid repair on the damaged wires.

*Where you come in:*
So I wonder if someone here could help me with a hookup for wiring diagrams? Ross-Tech says the Reference Circuit should be pinned to T60/29, so that's the circuit I want to trace. If there's a fuse or relay on that circuit somewhere, even better. Want to check everything.

Any other things I should test before I start pricing out a replacement ECU?


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## cylinder head o7k (Feb 13, 2021)

when you soldered or repaired the wires you may have changed the reference signal being sent back to the ecu. highly doubtful on bad ecu.


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## punkassjim (Sep 22, 2002)

cylinder head o7k said:


> when you soldered or repaired the wires you may have changed the reference signal being sent back to the ecu. highly doubtful on bad ecu.


How would I have changed the signal, and how can I change it back?


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## Ichabod0525 (Feb 11, 2018)

T60-29 looks to be the position for the 2.0L. 2.5 is different. Lets see how to attach this


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## cylinder head o7k (Feb 13, 2021)

punkassjim said:


> How would I have changed the signal, and how can I change it back?


by adding whatever you used to repair the wire you may have added a change to the reference voltage being to sent to or from the cps and map.. idk what the actual values are for each sensor but you could remove your fix and twist the two ends together to see what happens. after putting new sensors with the same results you should go back to the wires as the potential problem


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## punkassjim (Sep 22, 2002)

cylinder head o7k said:


> by adding whatever you used to repair the wire you may have added a change to the reference voltage being to sent to or from the cps and map.. idk what the actual values are for each sensor but you could remove your fix and twist the two ends together to see what happens. after putting new sensors with the same results you should go back to the wires as the potential problem


"Open circuit" is the issue. The reference voltage should be bang-on 5.0v even with the key off. I'm getting nothing at either sensor. The 5v reference circuit comes from the ECU pin T60/44, and branches out to the MAP, SAI sensor, and CPS (in that order).

I pulled the ECU last night, and while I'm not _entirely_ sure I got a solid contact at the pin, I'm pretty sure I was getting zero voltage from pin 44. So, while the wiring repairs are solid (again, tested with multimeter), the ECU is (seemingly) not putting out any voltage to that circuit.

Anything else that can be but a faulty ECU?


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## cylinder head o7k (Feb 13, 2021)

no doubt that you re attached the wires in a solid manner but i dont think you fried the ecu from having exposed wires from those sensors.


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## GTIVRon (Jul 24, 2009)

You sure the ECU is powered up with the key off?


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## Ichabod0525 (Feb 11, 2018)

I'm doubting that there would be 5v reference with Key off. It's not often that the 5v drivers would go bad in the ECU. It happens but I'd be double checking that and all the power & grounds to the ECU as well. Replacing the ECU is a PITA. Let us know!


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## punkassjim (Sep 22, 2002)

I've replaced the entire engine harness, from the ECU to the coilpacks. I've checked every fuse in the engine bay with a test light, and I've replaced both the Motronic relays. Same trouble code persists.

I got a new ECU from a junkyard. Not paired to my immobilizer yet, but still, I plugged it into my vehicle, cleared the previous car's trouble codes, and lo and behold: still throwing a "sensor reference b circuit open" trouble code. So, I'm convinced there's something else, somewhere, that needs to be checked, and it's not the ECU.

So. WTF else do I check?


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## Ichabod0525 (Feb 11, 2018)

I'm going on diagrams from a Jetta Model year from April 2010 on and it looks like the secondary air injection sensor shares that 5V reference with the intake manifold sensor and the camshaft position sensor. Try disconnecting each of the three sensors that share that 5V while watching the voltage, to see if one of them is pulling the circuit voltage down, focus on proving the fault. You'll find it.


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## punkassjim (Sep 22, 2002)

Hey, so, I've been in a very frustrating bang-head-against-wall mode on this issue, mostly due to cognitive/executive function issues. I wonder if you could walk me through, exactly, what you would do to "prove the fault." And, without complete wiring diagrams, I'm not sure where/how to check the power and grounds to the ECU, beyond testing the fuses and replacing the Motronic relays, which I've done. I'm not super handy with a multimeter, and I'd normally just go to the YouTubes to teach myself, but again…I'm having some cognitive/executive function issues, so I'm finding YouTube videos difficult to parse. But I think I can follow instructions, if they're specific to this case, and if they're written like I don't know much about electrical beyond measuring voltage between a power and a ground. So: what steps would you take to prove the fault?

I just replaced that final sensor (for the SAI) on the circuit, and it hasn't solved the issue. That's all the sensors, and the entire wiring loom replaced. I'm so very confused. The diagram you posted above shows the CPS shares a ground with the crank position sensor. Could that also be a culprit? I'm assuming the car would not run if the crank position sensor were faulty.


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## Ichabod0525 (Feb 11, 2018)

Disclamer- attempt the following at your own risk. Internet advice is worth just what you pay for it.

Locate the Camshaft position sensor.
Unplug it and turn the ignition key to the on position
Carefully test the plug
A meter measuring between pins 1 and 3 should give you 5v if not ...
Test pin 1 for 5v.
Test pin 3 for ground.
Do not probe pin 3.
What are the results?


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## punkassjim (Sep 22, 2002)

Hey Ichabod, can I ask a favor? The wiring diagram you posted before is helpful, but it's missing some data. The 5v reference circuit splits off to two other connections (follow tracks 197 and 201). I'm sure one of those goes to the SAI sensor, but I need to know where the other track leads. Feel like that's where my mystery lies. Can you screenshot those other pages for me? Thank you so much in advance! (CBUA engine code)

I tested the voltage at the ECU, MAP, Cam pos sensor, and SAI sensor. I'm getting a good 5v from ECU pin T60/44 (thank goodness), but only 0.8v at each sensor. Same readings whether plugged or unplugged, back-probe or terminal connection. Waiting on a new multimeter to replace my Harbor Freight garbage, so I can test resistance on the circuit.


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## Ichabod0525 (Feb 11, 2018)

Ok so a little confusing; Track 197 goes to the Secondary Air Injection Sensor 1 [shown as connector #5 on picture]. Track 201 is the same. They are both shown as production variations. 197 has the notes (Depending on equipment, Omitted as a running change) Track 201 has the note (running change) With the difference being the connector pinouts and wire colors but there should be only one or the other. Keeping in mind I'm going off diagrams for 2015. You may find some better with a search for 'Volkswagen 2009 Electrical Wiring Diagrams.pdf'


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## punkassjim (Sep 22, 2002)

Ok, so the ECU is putting out 0.7v (should be 5.0v) directly from pin T60/44, with all three sensors disconnected from the circuit, or connected, same results. And, testing from each of the sensor connectors, I get no voltage drop and no resistance to speak of. 

Disconnected the battery, swapped in a different ECU — not paired to the immobilizer, but completes all the circuits — and get the same 0.7v from pin T60/44 and from the sensor plugs. So, from that I can reasonably deduce that the ECU, the sensors, and the wiring to the sensors are not the problem. I even pulled apart the previous wiring loom to double-check that the circuit is as simple as it looks in the diagram. 

Anyone have a way of tracing which fuses or relays feed voltage to that pin? A buddy told me to check relay A1 and fuse SB10, and I did, but I wasn’t privy to the diagram he was getting that from.

I’d like to trace that circuit on a wiring diagram before I start tearing apart the fuse block. Anyone wanna help me find that spot in the wiring diagrams? I don’t see any detail upstream of pin T60/44 on the Shopkey wiring diagrams I’ve got on hand.


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