come on people!.. anyone got a WD (wiring diagram)..?

I was hoping someone on here might have a schematic or at least advise which pins to check for continuity etc. the 1.8T engine code is: AWU

I *think* from the T121 ECM / ECU connector to the relay J271 it uses the following:

T121/21 -->
T121/62 -->
T121/121 -->

but I'm not completely sure.. anyone able to confirm the above..and a good procedure for testing the relay wiring?

 

Manuals and diagrams here: http://workshop-manuals.com/volkswagen/


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thanks Billy - managed to get hold of a WD - albeit for a 1.8T AWP engine code (mines AWU) :

So, The Motronic Engine Control Module (ECM) voltage supply relay - J271 (# 428) - supplies voltage to the ignition coils with power output stages and the Engine Control Module (ECM) at pin 121 :

Pin T121/21 - 0,35 (Lilac wire) on ECU connector (harness side) -> J271 pin # 5/85 Signal
Pin T121/121 - 1,5 (Black/Lilac wire) on ECU connector (harness side) -> T2b/1 4,0 [Ignition Coils White/Red] -> J271 pin # 2/87 Switched Live (white/red wire)

J271 pin # 1/30 1,5 (Red/Grey wire) -> 3/86 gets switched power via 10a fuse S10

All fuses and wiring to and from the Relay Block to ECM tested out - power + 100% continuity / 0ohms resistance across signal wires etc.

With a Brand New Relay (which I tested also) .. I'm a little stumped now..

Next I'll test the Fuel Delivery.. but anyone got any pointers in the meantime?

 

So, there is a ground stud/point near the ECU/ECM wiring loom right next to where the ECU is mounted within the dash. Two ground / brown wires from each side of the ECU wiring loom ground there. I removed these 2x 'hoop grounds' properly cleaned both the stud and hoops with Wire Brush and re-seated / tightened the screw securely..

But, alas to no avail... (oh, and touch wood - my ECU has never been immersed / covered in water!)

So, other Relays I have under the dash are (from left to right) -

1. Dual Horn Relay -J4- Relay # 53
2. Load Reduction Relay -J59- Relay # 100
3. Not used / Empty
4. Fuel Pump (FP) Relay -J17- Relay # 409

Seeing as it is a 2002 model.. I'm gonna take each of these relays out and test each for good measure in any case.

I have a *hunch* the issue lies with the wiring loom for the Coil Packs.. maybe the ground..?

Pin T121/121 - 1,5 (Black/Lilac wire) on ECU connector (harness side) -> T2b/1 4,0 [Ignition Coils White/Red] -> J271 pin # 2/87 Switched Live (white/red wire)

as above .. "T2b/1 - 4,0 Ws/Ro" - white/red wire .. that is going to the ignition coils / coil packs?

-Just quickly checked.. 4-pin connector plugs on each of the coil packs:

Pin 1: Black /Violet strip wire -> ??
Pin 2: Solid Brown wire -> ??
Pin 3: Black /Blue or Black /Violet strip wire (seems to vary from Coil pack plug to plug?!) -> ??
Pin 4: Brown /Yellow strip wire -> ??

-Can anyone advise on the pin-outs of these Coil Pack connectors for testing purposes and / or anything obvious that I may have 'overlooked' ..?

i'm guessing either Pin 2 or Pin 4 is the ground wire for each of the Coil Pack plugs?

(on another note.. Back in the summer I changed the voltage regulator on the Alternator (wasn't charging) and I cleaned the main grounding point underneath the battery, so i know that's good)

 

Coil pack and wiring testing:

http://workshop-manuals.com/volkswagen/new_beetle_turbo_s/l4-1.8l_turbo_(awp)/powertrain_management/ignition_system/ignition_coil/component_information/testing_and_inspection/with_manufacturers_scan_tool/


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thanks Billy - great find :goodjob:

 

So, went off on a wild goose-chase for a bit :banghead:

The J271 / 428 ECU relay does NOT appear to be receiving the GND signal on Pin 5/85 from the ECU J220 T121/21 when ignition is on.

But here's the thing - there is 100% complete continuity / 0ohms resistance between the ECU J220 T121/21 -> J271 / 428 pin 5/85

Subsequently - there is +12v to not only the J271 / 428 ECU relay Pin 30, but also to Pin 3/86 (which is supposed to be switched via S10 10a fuse) Even with the keys out of the ignition

So, please- can anyone offer any pointers as to where this GND issue could lie? I've already cleaned and re-seated the GND point next to the ECU / J220 harness...

 

ok, so a bit more research and specifically, the ECU / J220 Pins 1 + 2 ground to Ground Connection points "607 + 131".

-Anyone have any idea where these GND points are located..?

 

ok, so just tried.. the car started for a bit and just died again.. not starting now though.

Seems like the J271 / #428 relay is getting intermittent ground on the control side.. however, the 5/85 wire checks out ok back to the ECU as mentioned.

come on folks.. anyone give me some pointers please - got to be an ECU grounding issue?

 

ok.. so I tried the ECU J271 / #428 relay in situ with an external ground wire wedged in / connected also to Pin 5/85 and still couldn't feel + hear the relay clicking on key-on. The ECU complained of :

"17070/P0686/001670 - ECM Power Relay Control Circuit (J271): Short to Ground"

So, I took out the relay and just bridged the "switch circuit" between Pins 30 + 87...

and the car fired up straight away! -[albeit complaining again about the above code]

Obviously, I now need to determine the cause of loss of signal from the ECU / J220 T121 on Pin 21 -> ECU relay J271 / #428 Pin 5/85

I cleaned both end points and cannot see any corrosion on the relay board or the ECU / wiring harness... + there's 100% continuity between these points.

-I guess the issue must lie further back in the wiring to some ECU grounding point(s)..?

Any pointers anyone..? or am I just compiling an "one-man" running commentary show

 

*Update*

ok so, several weeks on and off.. and I seem to be at an impasse. I have removed the ECU aka T121 / J220 and tested all connections as follows :

T121/1 - GND / Earth
T121/2 - GND / Earth
T121/3 - IGN Live +12v -> Fuse 29 / Fuel Pump Relay J17 # 409 / ECU Relay J271 / #428
T121/21 - GND / Earth Trigger -> ECU Relay J271 / #428 Pin 5/85
T121/62 - Permanent Live +12v -> +12v 10a S10 Fuse -> ECU Relay J271 / #428 Pin 3/86
T121/121 - IGN Live +12v -> +12v for ECU Relay J271 Pin 2/87
-> +12v for Ignition Coil Plugs Pin 1

So, Pin #21 is definitely the ground trigger output from the ECU to the ECU relay. However, it is currently seeing 12V+ with the IGN on or OFF, which I don't think is right..?

Consequently Pin #121 is supposed to be supplying +12v to the ECU relay + IGN Coil Plugs.. but there is no voltage at either of these points with IGN on and thus vehicle will NOT start, unless I *jump* the relay.

All wiring checks out ok - NO breaks between ECU -> relay -> IGN Coil Plugs etc and I have tried cleaning ALL the main grounding points (of which there are 3, GND 607, 608 + 609) near the ECU within the plenum chamber - BUT alas to no avail..

Don't know what else to check..

-Guys, anyone on here experienced anything similar or able to advise what else to check?

 

17925/P1517 - Ross-Tech Wiki

I personally haven't worked on that particular code or issue but if you are at the point, of thinking the ecu itself is faulty, you could ship it out for repair. From the above link and typical things to check; you seem to be down to the ecu itself? We have had members, have good feedback from bbareman for a ecu repair service; I believe they have a repair centre in the UK.

Home (GB) | BBA Reman

UK Office:
BBA-reman
Unit 1 Stirling Park
Laker Road
Rochester
Kent
ME1 3QR
United Kingdom
44 (0)1634 687222
Fax 44 (0)1634 864056
sales@bba-reman.com
Diagnostic equipment enquiries: diags@bba-reman.com
Please include this form with all repairs sent to BBA

 

yeah I know - I did think at one point that the ECU / ECM may be faulty!

BUT, VCDS diagnostics work fine and can communicate with all vehicle modules + when I jump / bypass the ECU relay it fires up just fine.

Now, I was thinking (although my head properly hurts now) I should start with the basics...

-What Sensor(s) gives the instruction to energise the ECU when vehicle is at "key on" stage and thus liven up the Earth output to T121/21 and therefore fire up the coil packs + injectors...? (no voltage currently)

Two things came to mind - Crankshaft Position Sensor (aka Engine / Vehicle Speed Sensor) + MAF (Mass Air Flow sensor)... Basic fuel metering is determined by these two sensors.

Since I replaced the VSS a few years back, thought I should start with the MAF .. so popped off the MAF connector, switched on the ignition and tested.

These are what the readings should be, followed by my readings in brackets:

Pin 2 + GND = +12v [no voltage]
Pin 2 + 3 = +12v [no voltage]
Pin 4 + GND = 5v [5v]
Pin 4 + 3 = 5v [5v]

So, the MAF was NOT getting any power!

-Does the MAF get its power via the Fuel Pump Relay...? (this appears to be working just fine, have tested it and even swapped it out for another)

Where is this connector E30 / 87a as per WD below?

 

I did not read all the comments in all the posts here.

I work on a lot of BMW's, far more than VW's and I know the BMW Immobilizer should inhibit the starter, fuel pump, ignition coils and fuel injectors.

BUT on BMW's of this vintage we have been seeing flaky keys that will allow a crank no start condition which at times has turned out to be a problem key and the immobilizer partially working or partially shutting/inhibiting systems. Usually the spark and fuel system would be inhibited and the starter was not, but should have been. Usually we find out the simple way if there is another spare key, we ask for the spare key and the engine will start.

So not to toss a monkey wrench in things, but to think about how the VW immobilizer works. I have never bothered to get in depth wit the VW immobilizer because I have never needed to.

Just something to consider, it may not even be relevant to this specific problem?

 

Thanks alot - but different key didn't do anything

At a Total LOSS now.

The MAF is now showing +12v on Pin2 on Key on. Reset ECU, tried to clear DTCs but these codes just keeping coming back:
----
2 Faults Found:

17987 - Throttle Actuator (J338)
P1579 - 35-00 - Adaptation Not Started
17069 - ECM Power Relay Control Circuit
P0685 - 35-00 - Open Circuit

Readiness: 0110 1101
----

Throttle Actuator DTC is because of this ECU relay not energising.

ECU / VCDS comms are fine, therefore I don't believe the ECU is faulty + when I jump the ECU relay everything is fine, although it complains of

""17070/P0686/001670 - ECM Power Relay Control Circuit (J271): Short to Ground"

The ECU relay is brand new (which I checked out also) and I've also cleaned up all the Ground Points.

All the Coil Pack wiring checks out ok too (no shorts) and have checked DVM contininity across all points.

The Coil Packs are just NOT receiving the +12v from the ECU T121/121 - hence no start.

Typically, this either means the ECU relay earth trigger wire is faulty or there is no power to the ECU itself.

But, I've checked this already .. and at the ECU harness itself :

T121/1 GND ok
T121/2 GND ok
T121/3 IGN +12v ok
T121/21 GND showing +12v @ harness (is that right?) (but NOT when J271 is jumped)
T121/62 +12v ok
T121/121 IGN +12v NO voltage! coming from -> +12v for ECU Relay J271 Pin 2/87
going to -> +12v for Ignition Coil Plugs Pin 1


-BUT when the ECU Relay J271 is jumped T121/121 'DOES' output +12v, like it should and it fires up!

So, it really sounds like a ECU relay J271 issue (which it isn't) as Pin 5/85 is not receiving it's voltage trigger from the ECU T121/21 (J271 5/85 shows .3v with IGN on)

To sum up - More likely its a faulty ground leading to the ecu to short out....

somewhere.... i think...Please can anyone advise?

 

Sounds like you've isolated the circuit and now you need to trace back to the source and look for damaged wires and/or connectors.

I've seen issues with burnt/shorted wires at the back of the fuse box, and also the specific 12v power source you are talking about should be fused, so look for any blown or failed fuses.

Also, what are you using to scan? I would highly recommend VCDS if you arent using it in this situation.

And, check the Ross-Tech Wiki for your code, may or may not apply: 17069/P0685 - Ross-Tech Wiki

 

Yep been using VCDS since ~2004!
Just to give an update - when these 1.8Ts are started the ECM / ECU also looks for a signal from the Crankshaft Position Sensor / Engine Speed Sensor (as with other VAG models). If this is missing it will not activate the Fuel Pump Relay thus preventing it from pumping fuel - in case of an accident where a fuel line gets ruptured, for example.

So, just to double check I pulled off Fuel-Supply Hose at the Fuel rail - and when I open the driver door or crank, a nice clean powerful supply of 99RON fuel pours out - therefore indicating the Fuel Relay, Fuel Pump and Crankshaft Position Sensor are fine.

I also checked all the main Ground Points, Fuses, Battery Voltage (~12.7v) and also just replaced the CTS (Coolant Temperature Sensor) with the 'Green Top' version as mine was the very old black version (that are prone to failing)

The Relay marked "100" which is located next to the ECU J271 relay, is in fact the Secondary Air Injection (SAI) Pump J299 Relay aka "100" relay. Have installed the revised 100 relay which is now # "644" light-green relay - part# 4H0951253 for anyone who needs to replace this. From the WD, I can see this has no bearing with the ECU relay anyway.

Anyway, I decided to manually short the ECU relay J271 to Ground by wedging a wire in Pin 5/85 (with the Relay in place) to the engine chassis. With the IGN turned on I still CANNOT feel the ECU relay clicking / closing. When manually shorting the ECU J271 Pin 5/85 relay to GND it reports the following:

4 Faults Found:

17987 - Throttle Actuator (J338)
P1579 - 35-00 - Adaptation Not Started
17070 - ECM Power Relay Control Circuit
P0686 - 35-00 - Short to GND
17925 - Power Supply Relay for ECU
P1517 - 35-00 - Electrical Malfunction
17953 - Throttle Valve Controller
P1545 - 35-10 - Malfunction - Intermittent

Readiness: 0110 1101


So, the ECU now also reports "DTC 17070 Short to GND" which usually indicates something is not getting power ie. circuit / connector disconnected

I removed the ECU J271 relay and measured the voltages at the relay holder:

1/30 = +12v Fused Battery Voltage -> exhibiting +12v with IGN on or off
5/85 = GND / Earth Trigger from ECU T121/21 -> exhibiting "0.5v" with IGN off and "0.35v" with IGN on
3/86 = +12v Switched IGN Voltage via S10 fuse -> exhibiting +12v with IGN on or OFF ('looped' from Pin 1/30 on the relay housing)
2/87 = Switched Live +12v to ECU / T121/121 -> exhibiting no voltage to T121/121 with Relay in place (because of GND trigger fault)

Thus - I take it as the ECU is not seeing a return resistance on the appropriate pin T121/121 from J271 Pin 2/87 it therefore reports that relay DTC.

-Whats strange about the above is Pin 5/85 is supposed to be receiving +12v trigger from the ECU T121/21 - it's exhibiting "0.5v" with IGN off and "0.35v" with IGN on ??

I have measured the ECU T121/21 at the harness (with the ECU out) and it IS outputting +12v trigger with the IGN on or off.
-to RECAP: there is NO break in the GND / Earth trigger wire between ECU T121/21 -> J271 relay 5/85

I tested at the ECU harness (with both the ECU + ECU relay out) BUT this time with the relay holder 'jumped' between Pins 1/30 + 2/87 (to simulate the relay energising / switch circuit closing) and measured at the ECU harness with IGN on:

T121/1 GND ok
T121/2 GND ok
T121/3 IGN +12v NO Voltage! (supposed to be showing +12v main power to ECU - Fuse 29 / S229 ok)
T121/21 GND NO Voltage! (outputs the +12v GND / Earth trigger to J271 relay at point of IGN on)
T121/62 +12v ok
T121/121 ok - now showing +12v as Relay has been 'jumped' thus -> +12v for Ignition Coil Plugs Pin 1 -> engine starts ok

Obviously a voltage drop would indicate that the live side of the wiring is faulty/corroded/damaged - I wonder, could the Ignition switch be exhibiting some kind of fault..?

 

Alright.

Well, I should have known better

Carrying out Static testing with a DVM / DVOM and no current flowing is **NOT** (cannot stress that enough!) a good way to test and verify end-to-end track paths / wires - as just one tiny strand of copper can get you the buzzer or voltage display on a meter!!

I should have loaded the track path / conducted a "Voltage drop test" to verify the incoming voltage to the ECU and other relevant wire's capability to carry current. Voltage Drop Test Results:

J271 / #428 Relay Pins:

1/30 -> 185mV drop (+12v Battery Voltage / Permanent live)
5/85 -> 253mV drop (GND / Earth Trigger from ECU T121/21)
3/86 -> 189mV drop (+12v Battery Voltage / Permanent live)

J220 / T121 ECU ECM:

1 -> 141mV drop (GND / earth)
2 -> 138mV drop (GND / earth)
3 -> 0.482v drop (IGN +12v)


Little concerned with the J271 relay GND / Earth Trigger wire @ 253mV drop - BUT...

WOAH - all this time - The power line to the ECU on Pin 3 @ 0.482v drop! -Nearly 1/2 volt DROP - which suggests there is resistance in the earth/ground path to the ECU.

I decided to remove the FUSE 29 (ECU Fuse) at the side panel, and conduct a voltage drop / Load test at both the left and right side terminals of the Fuse Holder independently.

-Right side Fuse Holder with Test Bulb in situ (incoming +12v supply) showed 290mV drop

-Left side Fuse Holder wire going to T121/3 (power wire to ECU) with Test Bulb in situ, showed 258mV drop


When combined - 290mV + 258mV voltage drop is the cause of this issue, by the time it reaches the ECU it's around 0.5v+ drop

I tried cleaning the FUSE 29 (ECU Fuse) holder contacts to no avail.. still has excessive resistance / losing a lot of current to ECU.

Gonna bite the bullet - and have to remove EVERY SINGLE GND + POWER POINT / CONNECTION on the Beetle and Clean and Check for corrosion.

I've already done the 3x GND Points near the ECU within the plenum chamber - next I'll check the GND point near the steering column and the one next to the IGN switch.

Also, the 'melting fuse box' thread is another place to check..

-Any other points to check ? ..and anyone know the track path for FUSE 29 / S229 - ie. which source wire the +12v comes from?

 

Unfortunately, been busy over the last 4-5 weeks and haven't had a chance to troubleshoot the ~0.5v Voltage drop at the ECU @ T121/3 on the beetle. Still off the road after ~3months..
and would really appreciate some help here..


Now, we really need it back up and running again.. and have looked at the WD and am a little confused. Working backwards from the ECU to determine this voltage drop.. it goes:


ECU T121/3 -> T6/1 [6-pin BROWN connector in plenum chamber] -> [A104] Plus connector -2- (15) in instrument panel wiring harness -> Fuse 29 / S229 15a -> [A2] Plus connection (15) in instrument panel wiring harness

I know where the T6/1 connector is (as per other post) and that connection / wire appears fine... so, where are these [A104] and [A2] connectors / connections..? Is this around the Ignition Switch.. as T121/3 is the Switched Live for the ECU..?

-Would anyone know, as it's a bit vague in the WD as per below:

 

Well.... you know

It's only been over a year since I last did an update on this pain-in-the-arse thread

ok

so. Long story short.

It turned out to be the one thing, THE one thing I was dreading THE MOST..

yeah, you guessed right.. the ECU was f***ed, I mean seriously fried

 

Brand new ECU from VW would have cost $$$$, and wouldn't have been economically viable since the vehicle is ~15years old etc etc

So, I set to trawling the web for a used one, knowing that I would have to find the EXACT same ECU with the EXACT same part number. Not easy.

Eventually found one on eBay.. thought that was hard enough.

But, that was relatively easy when compared with the next stage.

I wont bore you all with the intricate details, but suffice to say had to use an EEPROM programmer in conjunction with VCDS to exact and dump the SKU codes from both ECU's in order to programme across the immobiliser / ecu info... quite tricky

End result. The bug is working again

Cause of the issue?

IMHO, Electrical shorts cause by bad Earth points. Story with most VW's of that gen..

The main earth from battery to chassis was corroded pretty bad along with at the block too.

Done the "Big 3 Upgrade" so hopefully won't have any similar issue coming up again........

Now onto another issue. Will it or rather - does it ever end..

 

chassis ground



yea common issue is the battery chassis ground corroding . Glad you found the problem man.... good job.
thanks for posting pictures I had never seen the inside of the ECU in these cars,

 

no problem... but I cannot emphasise enough how important it is to have good solid Ground connections..

mine unfortunately was a worse case scenario.

Definitely recommend everyone think about doing the Big 3 upgrade..

I prefer to clean up the existing factory-wiring (and if it looks good - no corrosion), then implement Additional Wiring to the "BIG 3" Factory locations within the engine bay.

Most people just simply replace the factory stock wiring with thicker beefier gauge wiring.. but that's just my personal preference

I prefer *Adding* - because, as Electricity takes the path of least resistance - the more paths you have the less resistance / "bottle neck effect" + the Less chance of single point of failure!


1) Battery Charging Wire - Alternator positive to battery + / positive
2) Battery Ground - Battery negative to chassis Ground - goes to underneath the battery tray
3) Engine Ground - Engine Block to Chassis Ground

I did the above in addition to some others, and definitely noticed an improved Throttle Response and Idling also, as other VW and Audi owners have noted

As below, I added some extra 4awg cables to various points within the engine too from the Battery Ground Terminal:

 

I know this was some time ago, but just FYI, I am having the same problem, and I had the big 3 upgrade. But, I am starting with opening the ECU. Great work by the way.