99 S70 - Pesky P0136 code

krenekj · Post by **krenekj** » 11 Sep 2021, 10:37

99 S70, N/A, 221k, original owner, well maintained

I have a P0136 code that keeps coming back. I've run out of ideas and need some help.

The cat was replaced at 165k with a DEC unit from FCP - https://deccats.com/Product/DEC--EPA--V ... F8597349EA

Here is what I've done so far:

Both sensors replaced 3 years ago, 190k mi. with new Bosch units from FCP.
- P0136 code came up a few months ago
- Replaced rear O2 sensor with a new Bosch sensor (under warranty from FCP - thank you!), reset code
- Code comes back in first few miles of driving
- Take it to my mechanic - they find no exhaust leaks, an inactive ECM-220F code. ECM SW is up to date. They perform VIDA fault tracing and monitored the O2 sensor during warm up. It's within range. They suggest another brand O2 sensor
- Install a new Volvo rear O2 sensor, code comes back in the first few miles of driving
- Disconnect the negative battery terminal for 30 minutes (maybe it resets some electronics), clear the code, and it's back in the first few miles.

I'm at a loss. Other suggestions?

Thanks!

Post by **scot850** » 11 Sep 2021, 10:55

Try this thread and a linked one in it:

viewtopic.php?t=88488

Neil

krenekj · Post by **krenekj** » 11 Sep 2021, 22:16

Thanks for the pointer. I had seen/read that thread, but did not find any additional things that I have not tried (other than verifying the emissions system fuse). So, I'm still at a loss.

Any other ideas?

Thank you!

Post by **scot850** » 13 Sep 2021, 12:07

The issue may not be the cat, but the cat is picking up an issue elsewhere in the system.

There can be leaks in hoses or pipes which are affecting the reading the ECU is being fed. The exhaust manifold or flexi-pipe could be leaking.

Another possibility could be the ECU. I have had an issue with a 00 V70 NA where I had a bunch of codes and it turned out some were caused by corrosion on the ECU contacts. The dealer mechanics identified the issue, removed the ECU and TCU and cleaned them with electrical cleaner and refitted them 2 or 3 times to make sure any oxidation or dirt was removed from the contacts.

In my case this resolved some but not all the issues but at least started to make the process easier.

Neil.