P0155 Oxygen Sensor Heater Circuit

[fawtytoo]

The EM light has persisted so I guess I have to fix it. ECU code P0155: Oxygen Sensor Heater Circuit.

Question is (or questions):
1. What is it?
2. Where is it?
3. Is it easy to replace?

[Carolyn]

That's Bank 2,, sensor one.  It's in the exhaust manifold.

I stand to be corrected but I think the bank 2 sensor is the one to the left as you look at the engine.

This is a very common fault. 

A replacement Denso sensor is the ideal way to deal with this one.  You can buy one with the connector attached or a 'universal' one which uses crimp connectors to enable use of your old connector.  You can buy cheaper ones, but you'll wish you hadn't!  Denso is really the only way to go, as many members have discovered.

Both are readily available.  The complete one is around £60 and the DIY version is about half that price. 

If you have the original manifold with the heat shield, you'll also need a special socket tool for removal and insertion.  If you have an after market manifold a 22mm combi spanner will do the job.

see:

https://www.ebay.co.uk/itm/264087639366?hash=item3d7cd99546:g:cjUAAOSwUVFcE3uR&amdata=enc%3AAQAHAAAA4GRzjLtLRei0Vr2oP9EcbIxthExi2H4kl9Iawdo9HvijsOXTK1pzuL2hDrW0YAeSX6bVLSacTCgEjMdFaiquxvvVMMmOQsNRlMozwo%2FHLQB2Ip95L1WG0UUOQ5WFa79mFSUjjy95t1GIv1PkM%2F9iANJsPjIFKwuCCTEIYg%2BEhLVxThKzEQvfPWsM2uJhfwjmi4wSMCtTJbQIFcmqJMmcWdnm43Cwbq5rU9j4TbdDpzBdO7BgYOjARL4VywgnbqVM0WOkuIKI4YlzYNZp2tX8cVyr8Bv%2FgkhJDsbOB4eUtx1D%7Ctkp%3ABFBMxsaBtcBg

and:

https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2334524.m570.l1313&_nkw=o2+sensor+toyota+mr2+Denso&_sacat=34998&LH_TitleDesc=0&_osacat=34998&_odkw=o2+sensor+toyota+mr+2

[fawtytoo]

Thanks @Carolyn . Ordered the sensor and tool.

If it's a common fault, is it worth having a spare sensor?

[Joesson]

I replaced two sensors in the first year or so of my ownership after I had disturbed the OE manifold and I don't know what killed the one by the exhaust tail pipe but it died.
The other is an OE and had been fine for around 9 years *and the prices seem to have gone down in that time.
So I wouldn't keep a spare.
PS
*Nine years since replacing the other two but  I have no reason to believe it's not twenty years old as no record in extensive paper work that it has ever been replaced.