Club 80-90 Forums

Hi all,

I've completed a 2.0 AGG conversion in my '89 Syncro Microbus. Now I'm trying to add an Check Engine Light to my dash.

I'm a bit ignorant of the topic, but here's what I think I know.

The ECU has OBD1, with an early OBD2 connector (black one). I don't have an OBD1 reader, but understand that I can get fault codes by bridging the correct terminal. My problem is, there is no engine warning light to flash the fault codes.

Is it possible to add an CEL? Is it as simple as connecting LED to a terminal on the ECU, or is an additional circuit required?

Thank you in advance for any help.

If it’s an AGG then it’s as simple as using W/K lines for OBD socket. 

I am no expert on the AGG setup, but I have tried to decypher the crazy VW schematics.

From what I can tell you need two components for this.
1 - The MIL -
You need an LED circuit to illuminate.
If it is like most early MIL systems, then I am assuming that the LED is fed by an ignition live supply to the positive leg.
And grounded by the relevant pin on the ECU.
Ground trigger to LED negative leg.
I have seen mention of ECU pin 25 for this.

2 - EOBD / ALDL -
Typical early (pre-CAN) K line ECU diagnostics are connected at pin 7 of the 16 pin diagnostic plug.
From what I have read, this should be connected to ECU pin 43.

I cannot find definitive information about flashing out codes on the MIL with the AGG ECU.
All posts refer to using VagCom or VCDS to read codes. I assume any basic code reader should be able to read "generic" codes as all manufacturers use pin 7 for early EOBD1 diagnostics.

Thank you for the quick replies!

Seems then I only need to confirm what pin on ECU grounds the LED?

I have a Bosch 0 261 204 026 ECU with a 1HS 906 258 code. Not sure if that means anything to anyone?

JacobusRoux wrote: ↑14 May 2021, 19:19 Thank you for the quick replies!

Seems then I only need to confirm what pin on ECU grounds the LED?

Robsey wrote: ↑14 May 2021, 00:42 I have seen mention of ECU pin 25 for this.

Pin 25?

We’re trying to reinvent the wheel here. 
  VW put an OBD port in. It’s that simple. 
pin 25 is TPS related. Pin 10 if you’re desperate and bored with life. 

HI guys, 

@Elvis, not sure were on the same page. I want to install a Check Engine Light in my instrument cluster. As far as I can tell, this signal must come from ECU.

@Robsey, pin 25 on ECU, for me, is an output to switch the fuel pump relay. My best guess is pin 35 that has had its cable cut short. The best info I can get for this pin is that it goes to the instrument cluster. 

I think it depends on car model and year of manufacture.

MIL (A5) on instrument cluster on the Polo / Passat etc with AGG engine has 4 inputs.

Mil unit Pin 27 from vehicle speed sensor (B33) pin 2
White /blue.

Mil unit Pin 7 from ECU pin 11
Blue / white

Mil unit pin 10 from ECU pin 10
Violet or violet / white.
**** Which coincides with Elvis' statement above *****

Mil unit pin 26 to ECU pin 19
Green / black

Then diagnostic port (X1) is linked to ECU pin 43 via the immobiliser unit (A162)
Grey / white.

And that is all the schematic shows.

Blue/white is VSS on pin 11
Green/black is (digital) tacho signal on pin 14
W line on pin 43 is grey/white.

As previous - lilac/white on 10 is the badger.

Pin 35 is earth.

JacobusRoux wrote: ↑16 May 2021, 19:36 HI guys, 

@Elvis, not sure were on the same page. I want to install a Check Engine Light in my instrument cluster. As far as I can tell, this signal must come from ECU.

@Robsey, pin 25 on ECU, for me, is an output to switch the fuel pump relay. My best guess is pin 35 that has had its cable cut short. The best info I can get for this pin is that it goes to the instrument cluster. 

What year and model is it out of?
I’ve filleted feck knows how many AGG looms and have seen one small variance of colour in one wire/pin ever.

Hi guys, 

Thanks for comments.
Here's my 2.0 MP9 ecu pinout - as best I can figure it out:

1. Brown - Ground
   
2. Brown/Yellow - Throttle body pin 1
   
3. No Wire 
   
4. Blue/White - Injector 4 output
   
5. No Wire 
   
6. Black/Green - Injector 2 output
   
7. Green - Injector 1 output
   
8. Black/White - Distributor pickup +5V supply, pin 3
   
9. No Wire 
   
10. Purple/White - Throttle body pin 3
    
11. No Wire 
    
12. No Wire 
    
13. Yellow/Red - Distributor pickup output to ECU, pin 2
    
14. Blue/White - Throttle body pin 4
    
15. No Wire 
    
16. Blue/Black - Throttle body pin 8
    
17. Brown/Red - Ground
    
18. Yellow/Blue - MAP sensor pin 4
    
19. Yellow - Knock sensor pin 2
    
20. No Wire 
    
21. Red - Battery +12V supply
    
22. No Wire 
    
23. Black/Yellow - Ignition switch +12V supply
    
24. Green - Ignition control
    
25. Brown - Fuel pump relay
    
26. Red/Blue - Throttle body pin 2
    
27. No Wire 
    
28. Green/White - Injector 3 output
    
29. White - Diagnostic K-line
    
30. No Wire 
    
31. No Wire 
    
32. No Wire 
    
33. No Wire 
    
34. No Wire 
    
35. Blue/Red - To instrument panel?
    
36. No Wire 
    
37. White/Yellow - MAP sensor pin 3
    
38. No Wire 
    
39. White - Knock sensor pin 1
    
40. No Wire 
    
41. Grey/Green - Throttle body pin 5
    
42. Grey/Green - Engine coolant sensor
    
43. Grey/White - MAP sensor pin 2
    
44. No Wire 
    
45. Black  - Knock sensor pin 3
    

There's significant evidence that the wires have been fiddled with, and the colours may be non-standard. Pip 10 goes to the throttle body though?

Unfortunately, I'm not sure what year and model it is - nor is guy I bought it from. VCDS scan gives me: Part No: 1HS 906 258, Component:  2.0 MP9.0  26ZA0003 

Best off asking on SA golf forums if it’s MP9 chap.