Lamda fault code Single Plug conversion
 

Hi, I've done a single plug Saxo VTS conversion using the guide on here to splice the multi plug in the engine bay correctly from the VTS 3 plug,the only issue I have is a fault code for the Lambda P0157 intermittent, only comes on after the car is warmed up,the engine light does not come on.

As per guide I spliced the Lambda together with a ignition wire to get its positive from,I do have the correct black Lambda sensor for the single plug ECU and I do have voltage on the connector,I have around 800mv with the car running and I've 12v on the Lambda pins 1,2 and 3 and 8 volts on pin 4 with the ignition on,why am I getting the fault code? Not sure what else to check to be honest.

Car is not standard and it's currently running with the stock single plug ECU on a base map,I understand that the fuel map is not set up accurately but I wouldn't of thought I would get a fault code for the O2 sensor for this?

Also worth to note, I've got no reading on the cluster for the coolant temperature,I do have correct reading of the sensor using the odb, would the gauge not working on the clusters affect the 02 sensor? I thought it only cared about the ECU sensor, thank you.

Also,I was just thinking,is it not for the second O2 sensor the P0157 code? Looks like it is from what I can find.

The two white wires are heater supply and ground, so one should have 12v and the other 0v. The black wire is the sensor signal, and the grey is signal ground, so you should have 0.1-0.9 v on the black wire and 0v on the greay wire.

So i have 12v on one white wire and 0v on the other white one,i have 0.13v on the grey wire and 0.33v on the black signal,this is with the ignition on engine off.

That code is for the second lambda.

The coolant gauge wiring doesn't go to the ECU, so definitely has nothing to do with the lambda fault.
However, I have 2x J4 engines, with differing coolant temp sensors and loom connectors. The blue one (on my 3 plug) does the dash, the green one, does the ECU. Presuming you've wired them up correctly - as on a spare loom I have, it looks to be different - even though it's a three plug! I think it uses two wires on the gauge sensor, when my current one, utilises one wire.

Yeah,i found the same thing,picture below,if it is for the second lambda then it's not much of my concern,i have a single plug and that only uses one lambda sensor.
For the coolant gauge then thats a separate issue,i'll investigate more at some point,i do have the reading on the ecu trough diagnostic and have a stack gauge to keep an eye on temps anyway.