I have a 2005 ST 4.2 l and replaced the a/f sensors both in front. Denso 234-9030. Still have the MIL popping. Replaced the relay just in case. Still on. Any ideas on what I might be missing?

 

P0031 isn't a MAF code. Grab the free codes PDF / JTIS and see what the known causes are.

 

My OBD II says HO2s Heater Control Circuit Low Bank 1, Sensor 1. The MAF could be a possibility as I got O2 type codes when my Disco II MAF failed.

 

If that's logic.... words fail me.

 

When reviewing the response, I thought it was stated as it was a MAF code. I miss read the reply. And yes, MAF failures throw o2 sensor failure type codes in discovery II.

I replaced both upstream sensors and still have the code appearing. If anyone has run across this issue, please let me know how you sorted the problem.

 

My S type has the same problem. Failure of the ECM. Replaced and all sorted. Jag shop said he had seen the problem before but had been unable to correct for other customers.