I have a 2003 XKR with code p1646 which has been working on this code for some time now. This code is for the pre heaters on the upstream oxygen sensor on bank 1, or the passenger side. I have replaced the sensor several times, with no change. I tried to change the drivers side O2 sensor also. Then I tried the downstream sensor, no change. I also checked the fuses on the passenger side under bonnet fuse panel #1 and #14 which are part of the O2 sensor system. Any good suggestions?

 

I’ve never had this problem but I think....

Are you sure of the new sensors installed, Denso etc?, as members have reported putting in wrong replacement HO2S sensors? Other members may chime in on the resistance values expected. Note our sensors have pre-heating circuits built into the sensor, to get it to operating temp.

I would also check the wiring from sensor to their connection pins. Maybe a broken wire or short somewhere.

IMHO Worst case is that your ECM is on the way out.

 

Assuming a quality replacement HO2S has been used, you must have eliminated heater failure as the P1646 cause which leaves two other possibilities:

1. HO2S sensing circuit - short circuit to ground, short circuit to high voltage, open circuit or high resistance
2. ECM Failure

Given that ECM failure would also give several other issues, a circuit fault is the more probable. The first part to check and eliminate is the harness connector.

Graham

 

What I have done so far. I have replaced the O2 sensor with an expensive Denso O2 sensor. It was ordered from Ebay in new condition and the gray connector connected just fine. There is no apparent damage on the wiring harness side of things. I checked fuses # 1 and #14. Neither was shorted out. I have had some other issues, and other codes from time to time, but all have cleared, except the p1646 code. I have tried two or three other O2 sensors. I tried replacing the drivers side o2 sensor. I have also replaced the downstream O2 sensor on the passenger side. The other sensors are new, and of various brands. The car does have issues with a misfire, that only seems apparent at idle.

 

Check the ohms across various of the parts of (*) the new sensor then check them at various parts of the circuitry until you reach the PCM (aka ECM). They should not change much but fair chance they will and that'll point to where there's a fault.

(*) I suppose you can do just the heater pair

 

What about the relay? These brown relays are all the same, so you can swap them around to test...

Best of luck, keep us posted.

 

Where are these relays? Where are these points to check the ohms? Get further up the wires path, but were exactly?
My mechanic at one point suggested it could be the opposite O2 sensor. So I swapped out the left upstream and got p1646 code. Then I tried downstream right sensor and now have code P0037. I put the old sensor back, but still have the P0037. It's getting worse! On the plus side, the car is actually running better.

 

Go to jagrepair.com and find the 2003 electrical diagram. There are several codes manuals as well. EVERYTHING electrical is documented there, horse's mouth and all that.

 

Hi.
Take a look here:


https://www.jaguarforums.com/forum/x...highlight=1646

 

+1

P1646 doesn't accuse the associated relay directly, but if the sensor heater isn't getting power then the car can't sense the current it isn't drawing. It may not do that directly, but it's worth a $0 try.



Try swapping the relays over to see if the code changes. They are here: