Imagine my surprise when I hooked up an ELM327 scanner and found out it doesn’t work.
I had to figure something out. After scouring through the workshop manual and wiring diagrams I was finally able to figure out what’s what.
Info
I also documented this on pakwheels
A bit of facts
Baleno came in 2 variants:
- With oxygen sensor (referred to as G13/G16 with WU TWC in the manual)
- Without oxygen sensor (referred to as G13/G16 without WU TWC in the manual)
Ours is the second one. Without Oxygen sensor.
The ECM was different for these variants.
ECM with O2 sensor
ECM without O2 sensor
Both have different pinouts. One you can already guess is to have the wiring for O2 sensor, but there’s another big difference which is relevant to us.
ECM with O2 sensor interesting pinouts.
ECM without O2 sensor ECM pinouts.
Ayoooooooo. So:
- In ECM without O2 sensor, there is only one DLC output by the name SDL
- In ECM with O2 sensor, there are two DLC outputs, Data link connector (5V) and Data link connector (12V)
Looking at the voltage level for SDL, we see
So it’s about 5V, which matches one of the DLC pins in ECM with O2 sensor. So they’re the same.
So what we can conclude is:
- ECM with O2 sensor has two DLC
- ECM without O2 sensor has only one of the DLC (5V)
Analyzing wiring diagrams
Now, to add more context, let’s go over the wiring diagram pinout for the OBD port (SAE J1962) and these DLC outputs to see where these pins end up on the OBD port.
OBD port (SAE J1962)
ECM - DLC wiring for O2 equipped vehicle
ECM - DLC wiring for without O2 equipped vehicle
There is only the SDL going to pin 9 of OBD port.
Immobilizer equipped vehicle without O2 sensor
Pretty much the same except that ICM (Immobilizer Control Module) is also now linked with the SDL line.
Info
On immobilizer equipped car with the O2 sensor, they also did not add DLC (12V) going to pin 7 of OBD port. It’s the same as immobilizer equipped car without O2 sensor.
Conclusion
So the DLC (12V) goes to pin 7 of OBD port, which from standard is going to be an open standard for K-line (ISO 9141-2 etc).
Pin 9 of OBD port is left up to the manufacturer to do whatever they want. This is called SDL in the wiring diagrams (Serial Data Line).
Further steps
So we’re in a tricky situation. The ECM in my car only provides the SDL wire to pin 9 of OBD port. This protocol is proprietary hence ELM327 scanners will not work with it.
So if we want any chance of interacting with ECM from OBD port, we need to investigate about SDL protocol and figure out how to use it.