Hi folks

I’m normally over on the X300 section but am currently trying to help a friend of a friend with his 99 XK8 (UK). I’m just looking for some experienced eyes to validate my thoughts.

Here’s the background story. He purchased the car at auction about a year ago. His experience is rich running since purchase – smells of petrol, very poor economy, black tail pipes – but performs well. The Check Engine light is off (more about that later). The car stays in Open Loop always.

Reading codes it only has P16146 and P1647. These are for upstream sensor heater circuit for Bank 1 and Bank 2. I have done some testing. The heater relay is good – inputs and outputs. I have tested power and ground for heater at the O2 sensor connector (Bank 1). I get 10.3 volts with ign on and 0 with ign off (seems reasonable for PWM signal?). So I’m confident the wiring to the sensor and the inputs to the heater are good.

I tested resistance of the heater pins on the Bank 1 sensor (unplugged). It read 1.7ohms – I was hoping it would be open or dead short, but the reading looks like it is feasible – this is cold and engine off. I have to assume the issue is intermittent and maybe goes open when hot, as the codes do not re-appear immediately when engine runs but do after a few minutes.



I’ve told him he needs 2 new upstream sensors.

Would that be your conclusion also? Or have I missed something.



More background. The O2 sensors look like they have been replaced already. I’m guessing someone has done that but maybe fitted cheapo sensors or the wrong type. The Check Engine light is not on – it should be – the O2 sensor codes above should set the MIL.

Diagnostics say the MIL is on – but it isn’t. I think someone may have frigged the light and wired into something else – like ABS light? Just guessing.



Any thoughts appreciated.

 

Faulty MAFS is a possibility.

 

Genuine Denso sensors are an absolute must. Anything else is a crapshoot and may indeed be causing the issues you described....

 

Brendan, you look to be right (sadly).