FYI - Here is the OBD2 ECU and TCU pinouts:
http://www.alcyone.org.uk/ssm/obd2pinout.pdf
Anyways, I am trying to make the P1702 check engine light come on to see how and when it happens. I cut the signal from the ECU Pin 80 (AT diagnosis data waveform), and it didn't throw a check engine light. I drove around the block a couple of times and let the car warm up, and no CEL. I drove it around again today with it cut and still nothing. I actually went and disconnected the entire TCU harness (3 connectors worth) and drove the car around again. It drove fine around the block and still had no CEL.
Any ideas why the CEL isn't turning on for this? My OBD2 scanner had no current or pending codes. People clearly get the P1702 when they do 5MT swaps, so I wonder if it is a combination of factors that cause it to be thrown? And not just the one wire serial stream?
My plan was to
- Cut the TCU<->ECU diagnosis signal and get CEL
- Clear CEL code
- Use Ardunio to transmit in the 750ms pattern I recorded during regular operation.
- Hope that CEL does not go on with Arduino running
- Do 5MT and use Arduino to keep the CEL off
Here is the cut wire with spade terminals for easy reconnection, and connection to an Arduino for logging the TCU, or emulating a TCU signal into the ECU:
