Originally posted by smally
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It's not a stand alone trans ECU. It's all in the engine ECU. I've been going through the wiring diagrams (WDM) to find where the SPD signal is derived. It's a bit confusing.
The speed sensor is connected to the ECU at D14 and D28 in your model. It is probably a pulse input (REF WDM 19 zone 4). The SPD output (actually called SP1 on your model) is on ECU B22 (Ref wire V-R, WDM 14 zone 4). It's shown as an input but I suspect not.
All SPD connections are best shown on the combination meter in WDM 55 zone 5 (wire colour V-R). This WDM shows it fed off to all the other accessories requiring SPD input, including the ECU which is the one of interest for the A/T shift points. This WDM seems to be suggesting the combination meter provides the SPD output. If so, the speed sensor data in the ECU must get to the combination meter is some other mysterious way. I can't see how. This is why I suspect it is an analog output from the ECU based on it's speed sensor pulsed inputs. If so this would prevent you doing anything with it to alter shift points.
If on the other hand the combination meter is the SPD output then the analog SPD input to the ECU would be pretty easy to modify to play with your shift points.
Hence you need to confirm whether ECU B22 is an input or output. I would first put an analog meter on it to ground, go for a drive and confirm that it is an analog signal, where volts are proportional to speed. Then it's a matter of putting a low resistance in series and check the polarity across it. That will tell you if it is input or output. If you get no voltage drop increase the resistance.
Are you with me so far?
Cheers
Bob
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