If the car ran after the timing belt replacement then no need to look at that unless it jumped a tooth but a P0036 is a heated oxygen sensor related. As far as I know even with a faulty Oxygen sensor is should still start. MY V70 did always start with a faulty oxygen sensor. Did you reset the code b...

What engine do you have?
Did you change the timing belt yourself?
If so, how was this changed?
With cam locking tools?

Have the codes been read to see which cylinder is misfiring?
When known then change the ignition coils around to see if another cylinder starts misfiring to find out if it is a faulty coil.

Maybe this topic on this website has some info?

http://www.volvoforums.org.uk/showthrea ... cem+repair

The timing belt has not been checked and I don't believe has been changed. The car belongs to my son's girlfriend so I have a hard time committing to troubleshooting it. Hence the more than 30 days sitting. I have little experience with timing belts or timing in general. A mechanic told me that if ...

Did you work on the timing belt before the non starter?

In case it is an electrical problem:
I read an item on a UK Volvo forum regarding the wiring loom underneath the radiator that can cause some strange faults.

I hope it's ok to add the link , if not then please remove it.

http://www.volvoforums.org.uk/showthrea ... =wire+loom

I had some time this weekend to get to the ECU for my P0340 error. I disconnected the plug and checked the wires of the camshaft positioning sensor and these are all three ok I have opened the ECU itself to see if there are any cracks on the printed circuit board but can not find any ( I've looked w...

Good morning, I have purchased a 2003 Volvo S40 1.8 Petrol non Turbo after selling my V70 last year. This S40 has now developed a P0340 error. Engine management light is on. When I reset the light it comes back after the second time starting Car drives ok but is slow below 3000 rpm I have changed th...

You can maybe find out on this website if the car has one or two sensors

http://www.lambdasensor.co.uk/main/mindex.htm

Search on type of car and engine and see if it mentions a rear sensor
My 1998 NA V70 has only 1 sensor (B5252S) but my 1998 XC 70 AWD has two (B5254T)