I have to wonder how true this is. I have used early ECUs in some later models without a problem. Since my spare ECUs that are wired for the Digitool are both early types, I use them when troubleshooting. I may have only used them in up to 89s though. The 2 added wires appear to me to be simply for the ECU Malfunction light that VW briefly added to some 88/89 models. 90/91 did away with the light but the wires are still in the harness. 97.123 shows ECU pin 20 wired to dash and connected to an ECS-Malfunction light and switch (88/89) 97.205 shows ECU pin 20 still wired up to dash area but not connected to anything anymore (90+) 97.105 shows ECU pin 20 not used (87) , same for both 86 wiring versions Pin 23 is also used in (88/89) and (90+). It connects a secondary power source to the ECU when the key is on even if the ECU power relay is not functioning. I presume this is to allow for the ECU to detect missing main power and allow error codes to still be displayed, such as a code for "bad ECU relay power". A change was made to the relay and it's wiring to accomplish this. As far as I know, no error codes were actually implemented in our Vanagons. OBD was coming and VW seemed to be getting ready for it's implementation. Mark
Eric Zeno wrote: > YES. There are several differences. IF you look at the wiring, > alone > you will see that there is , IIRC, 2 added wires to the ECU. An older > sat, 1986 ECU will not run a 1990 model. > Eric |
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