Hi all... So, I have the P1646 code. I put in a new denso O2 sensor and still have the 1646 code. I also installed a new knock sensor as that code also came on. I just can't get that 1646 code to go away! All the wires look to be clean and not broken. A mechanic told me he thinks it is the ECU. I don't think so as this is the only code that comes up. The ca runs great. It's a 2000 XJ8... VP..
I am at my witts end....
Thanks

 

It takes a couple of drive cycles for the code to clear.
Denso is the one to get for sure,

Heated Oxygen Sensor, Upstream
Jaguar P/N: Other P/N
XR86938: NTK XR86938
C2C29250: Denso DOX-428
C2P8810: Denso DOX-426

 

What is a drive cycle? I did just drive the car about four miles. I gusse what I'm asking is there something special I should be doing? I've also tested every relay and every fuse including the ones next to the ecu..

 

You have to drive the car at a maintained speed above 40 MPH for up to 10 miles. The ECU has to read the functions and determine that the issue has been resolved before it resets.

 

On a LHD car, P1646 is for the passenger side upstream sensor. Did you replace the D/S or P/S upstream sensor?

 

Pass side...

 

I'll try that tonight and I'll let you know. Thanks

 

P1646
ECM HO2S control malfunction –
A bank, upstream

HO2S heater failure
HO2S sensing circuit short circuit to
ground or high voltage
HO2S sensing circuit open circuit
ECM failure

 

Is it possible that both upstream 02 sensors have been plugged in the wrong connector?? Maybe by accident somebody in the past had plugged the D/S (B2) upstream sensor into the P/S (B1) harness connector??
Probably one of the easiest tests to perform is on the sensor connector, unplug and find the 2 silver female pins and ohm them out. They’ll be the 2 black wires connected to the 2 silver female pins. If it’s bad, it will read open loop or no continuity. That’s the heater circuit for that sensor. If memory serves me correctly, I believe it was about 3-4 ohms of resistance on a new, uninstalled Denso sensor.

 

The pic is from this link post #2.... https://www.jaguarforums.com/forum/x...cement-195018/

 

I just tested the wires from the sensor plug back to the ecu and I have continuity on them all. The black wires have 5 oms. it is a new denso o2 sensor...I am lost...
Thanks for your help

 

Swap the new one side to side to see if the code follows it.
I generally replace both O2 sensors when I get a O2 sensor code. The thinking is both sensors have seen the same use and if one has failed how far behind is the other one?

The other factor is it's not much additional work to change the second one after you have raised the car and removed the under body panels. So your right there anyway. And I hate going back into the same area to do a repair twice.

Have you been clearing the code before you drive around some?
.
.
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If fixed, the code should self-clear after 4 warm ups.

If you clear codes via an OBD tool it may take 2 warm ups to flag the code if the fault persists (but more likely just one short drive).

It's true that P1646 doesn't have to be the sensor but it very nearly always is.

Lots of good advice above so don't despair!

 

verify circuit continuity from connector to connector, swap O2s bank to bank. if everything’s good it probably needs an ECM. seen it before

 

Working in a large Jaguar shop or dealer, it was easy to diagnose a fault like this.
Test all the components and circuits before swapping ECMs and if the circuits are good but the fault won't CLEAR, (HARD FAULT) then try the ECM in another car with NO FAULTS to see if the DTCs will clear.

If the fault follows the module, you have your answer.

I have found faults follow an ECM for things like CMPS and other sensors.
Output Semiconductors can be overloaded and fail.

 

I just switched the upstream o2"s from side to side and the P1646 code remains. Now i do have a extra ecu from another XJ8 but it's not going to work without having it programed. So I'm back to square one... lost

 

I just swapped sides with the sensors and the P1646 code came up still... Does that mean the ecm is bad?

 

I guess I would be checking the wiring from the new O2 sensor, particularly each blade . . .

 

I had an intermittent O2 sensor code on my first 2000 VDP that turned out to be the wire that connects at the ECU. If it's back 1 it's connected at the ECU at connector EM 85-01 or Bank 2 EM 85-2. The crimp on the wire in the connector on my car was weak. I ended up cutting off the EM85 connector from a junk car and soldering it in. EM 85 is the right hand connector with the heavy looking wires.

 

lucky guy, mines driver side and it will always be something that should be fixed but ain't gonna be.