P0036 and P0136 O2 sensor issue 1999 S70 T5

Post by **Eddystone** » 15 Feb 2019, 15:42

Found a post by Lee that says this:

"P0036 is a front O2 sensor heater circuit failure. It is either a wiring problem or a bad heater. The only way to fix the bad heater is to replace the sensor. P0136 is a bad reading from the rear O2 sensor. Wiring, a bad connection at the connector, or a bad sensor."

My code reader says:

P0036 H02S Heater Control Circuit (Bank 1 Sensor 2)
P0136 HO2S Sensor Circuit Malfunction (Bank 1 Sensor 2)

Which sounds like both codes point at the same sensor.

Nice warm day today near Philadelphia - and it's raining.

These are the codes I have. What's the usual cause of this? Defective O2 sensor? Bad connector? Vacuum leak?

Sounds like a hardware failure, but recent experience with a BMW tells me a vacuum leak might be just as likely.

Post by **wizechatmgr** » 15 Feb 2019, 20:56

I'd unplug the connection to the car's harness and clean corrosion, then plug it back in. Clear the codes and see what you get.

I'm not sure on this particular O2 sensor, but it is possible that both the heater circuit and the sensor circuit share a common ground - if so, corrosion on the ground would potentially cause both to trigger. Someone with more "senior" experience in Volvoland can either confirm/deny this one...

Post by **abscate** » 16 Feb 2019, 05:24

Which car is this?

Put year and model into title please, if possible

See 5 posts down in this thread

viewtopic.php?f=1&t=81171

Post by **Eddystone** » 16 Feb 2019, 05:30

99 S70 T5
Topic title updated

Post by **Eddystone** » 16 Feb 2019, 05:36

abscate wrote: ↑16 Feb 2019, 05:24 See 5 posts down in this thread

viewtopic.php?f=1&t=81171

"So, after replacing that main ECU relay that looked burnt, nothing changed. However, I noticed that the Emissions Systems fuse (20A) was blown. Replaced the fuse, and instantly the car was running MUCH better (it was stumbling a bit, noticeable breakup in the exhaust). Within minutes, the CEL turned itself off."

Assume this is what you are referring to. Will check that out. Will have to do some research to know where that fuse is...
Looks like #5

: 9.png (361.92 KiB) Viewed 2363 times

Will also check connector. Where is "Bank 1 Sensor 2" located? Looks like the connectors for both sensors terminate under the master cylinder in the engine compartment. https://cdn4.pelicanparts.com/techartic ... /pic02.jpg
This is for a non-turbo, but may be the same for mine. A starting place for my search.
https://www.pelicanparts.com/techarticl ... cement.htm

Is there more than one "bank" on this car? Is Sensor 1 before the CAT and Sensor 2 after the CAT? What's the arrangement?

Post by **abscate** » 16 Feb 2019, 05:50

There is only one bank on these cars ( bank refers to separate exhaust manifolds like a V8)

Sensor 1 upstream, sensor 2 downstream

My BMW M54 inline 6 has two banks though, since the two exhaust manifolds are separate. That means 4 OXS on that puppy.

Post by **Eddystone** » 16 Feb 2019, 06:29

abscate wrote: ↑16 Feb 2019, 05:50 There is only one bank on these cars ( bank refers to separate exhaust manifolds like a V8)

Sensor 1 upstream, sensor 2 downstream

My BMW M54 inline 6 has two banks though, since the two exhaust manifolds are separate. That means 4 OXS on that puppy.

Coincidentally, my only other O2 sensor experience was with a BMW M46, so I know what you are talking about. On that car, the real problem was a leak in air intake after the MAF sensor. I built a home made smoke machine that worked like a charm. It's a glass pickle jar with a soldering iron JB Welded into the lid and some J&J baby oil. Works amazingly well when pumped into the brake servo hose. I've been meaning to do that with both of my P80s just to see what leaks I might find.

I'll look at the fuse and clean the O2 connectors, then maybe look for vacuum leaks. That #2 sensor looks pretty hard to get at.