Any auto gearbox experts here?

I'm having a acouple of odd issues. First of all I'm getting a P1600, no communication with TCM fault from the ECM. Looking at the serial data line between the modules with an oscilloscope I see data, what looks like 6 bytes, a pause then maybe 3 bytes. If I disconnect the TCM I get just the 6 bytes, so presumably the first bytes are the ECM talking to the TCM and the 3 bytes are the TCM's reply. This looks like the two modules are communicating. However it does not agree with the service manual I downloaded which says the data is one way from the TCM.

When driving it shifts up correctly but I'm getting harsh down shifts, with the engine sometimes revving quite high for a second or two, as if it is losing drive. I did recently flush the gearbox oil and change the filter. Unfortunately with the P1600 fault I can't get any other gearbox fault codes.

Does anyone have any pointers?

I just looked up P1600, here is the text

P1600 SUZUKI Code - Engine Control Module Supply Voltage Low From Ignition Switch

|P1600 SUZUKI code possible causes

Faulty Engine Control Module (ECM)
Engine Control Module (ECM) harness is open or shorted
Engine Control Module (ECM) circuit poor electrical connection

That suggests that the ECM is not getting powered correctly, perhaps a wiring or connector fault or really low battery/charge system?

Other lists for P1600 suggest the battery back up for long term memory is low.

Thanks. The battery is good and both ECM and TCM have good power and ground. The two modules communicate over one wire. With both modules plugged in I can see data on both ends of the wire (by probing the relevant connector pins).

Looking at the data going along the wire with the TCM plugged in and not plugged in it does appear that the two modules are talking to each other. That's what I find rather confusing.

I found the TCM diagnostic connector today and it just reports code 12 - no faults found.
I took it for a decent run today and the down shifts seem to be getting a bit better. Either that or I'm getting more used to driving around the problem.

I've not had mine long enough for diagnosis but it should be completely smooth up and down.

What Jimny you have?
If it is JB43 2005+ then ECM+TCM communicate over TWO wires - red (terminal E118-7) and white (E118-. These are high and low CAN bus terminals (do not remember exactly who is who).

 

Secondly service manual says that both module send data to each other.