HELP... I got the P1646 code. I bought the right Denco o2 and installed it. The code keeps coming back. I took it to good mechanic and he seems to think the ECU. has a short in it. I don't really think thats it. So, has anyone have an idea what I could do to check it or better yet, get rid of the code?
Thanks very much...
Curley

 

Interesting. You have the P1646 on the X308, I have it since quite some time on my 2.5L X-Type.
I put a new O2 sensor in (for the second time now), but cannot report yet, if that improved the situation, as I have currently drained the engine oil - I am about to swap the sump gasket.
I'll let you know, if there is an update on my side - and hopefully I will learn something from your findings...

 

See page 41

The O2 sensor heating element can be easily checked for resistance against the other front sensor

AJ27_ECM_2000.pdf

What year and engine ? AJ26 or AJ27 ?

The ECU provides a ground for the heating element to heat up the sensor to read properly ( sensor physics )

For a 2000 with a AJ27 see page 101

X300 00/E COVER

Blue / Yellow and White / Green wires on the fwd bank 2 sensor connector

Red / Blue and White / Green for the bank 1 sensor connector

 

More info needed I think.

What year and model is your car? We don't know if you're driving a 1998 XJ8 or a 2003 XJR. If you have an AJ27 powered supercharged car, the 1646 does NOT mean you have an O2 sensor problem at all, it means you have a relay problem with fuel pump #2...I know this because I replaced my O2 sensor to resolve a 1646 and the code didn't resolve until I found out from some smart people here that I needed to replace my fuel pump #2 relay.

What sensor did you buy and where did you install it? There are 4 O2 sensors in the V8 cars, I know you said you bought the right one and assume you put in the right place, but its easy for people to get turned around, especially if they look at the car differently, like for example if you found code 1646was for the driver's side O2 sensor, that would only be correct in a right hand drive model like in the UK or Japan.

I'm very skeptical of an ECU failure so specific that it throws this code and yet still runs the engine properly, operates the gauges, shifts the trans, etc. Much more likely either your own error or a bad wire somewhere in the sensor harness. Not criticizing you or your skill, I don't know you...but I do know my own skill level and I've messed up seemingly simple things in the past.

 

I have an XJ8,2000. I too find it hard to believe the ECU has a short in it. I'll look into it more. Thank you for getting back to me. I had this problem a year ago and I changed a few relays and all was good. I did change a few relays this time but maybe I had another bad relay... I'll try some new ones and see what happens...
Thanks again...

 

Check the wiring to the left sensor, upstream; if wire has broken, you will get 1646. What happens when you remove the code?

 

Also can swap the connectors from the left to the right, so the left sensor is plugged into the right side harness and vice-versa. If the 1646 persists, the problem is likely between the connector and the ECU, if it changes to a 1647, its the sensor or the sensor's wiring pigtail.