Hey I own a Jaguar xk8 2001 coupe

I just replaced the toughest sensor I ever did I swear. And after putting in the new denso sensor it's still saying code 1646.

A little context, I took two days getting the old one off. I replaced sparkplugs while I had the intake off and after putting everything back and unplugging the sensor (it was cut off in the effort to replace it) the car idle was very rough and the brakes were hard and stiff like the brake booster wasn't even working proper. It gave codes such as low and high circuit to the O2 sensor (bank one upstream) because it was disconnected so I knew it was definitely what I was working on

Nonetheless, I continued and managed to get the new part in, plugged it up. Cleared codes and let the car sit with the battery disconnected for an hour. Afterwards I plugged it back up and started it. Still rough idle, like the car shakes idle. Drove it around up to temp, the brake were still hard and codes came back for 1646 the same code... Again. Could I have possibly tripped a relay/fuse? Is there one associated with it? Could this fuse also be in relation to the brake booster?
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verify wiring to ecm. if good replace ecm. denso cup sensors have a lot of elaborate circuitry to check their performance

 

Are you certain you received a genuine Denso sensor, and is it indeed the correct part number for that specific application? Lots of poor-quality fake Denso sensors being sold online these days....

 

Honestly I'm starting to think this myself. I'm going order one off of rockauto where they are for sure checked to be genuine. The price on there is 215$ for the sensor but it'll be worth it to know. ( The one I bought previously was 150$ I guess could've been fake )As for the rough idle it could be one my coils I replaced which I'll change out and check if that's whats causing the rough idle as well.

As for the brake booster I'm still not sure. I'm going to check the fuses and see. I feel as if it may be a part of the damping module. And maybe the fuse blew giving low power to it. It's raining today so I'm waiting for things to calm down before accessing the issues once again

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I know what you are talking about - I changed mine last year, it is a real PITA.
Idle rough and no vacuum to the brake booster, and you say you had the intake off? Sounds like a major vacuum leak.

 

Yep, what did you do to remedy this? Or some possible things I should check to see why this is happening.

 

I had a hard time replacing the O2 sensor, but did not touch anything else, and had no trouble codes or fault after that.
I always suspect the last thing that was done to a car when faults occurs.
To check for vacuum leaks you can use some starting fluid, brake cleaner or other highly flammable liquid and spray it around the intake, pipes and hoses that is connected while the engine idles. If there is a leak you will hear the engine respond. If that sounds scary, you can use a smoke machine to fill the intake system with smoke and see where it comes out.

 

I ended up finding the issue yesterday. It's this hose with a red button near the fire wall on the passenger side. It's sensitive so if it turns even a bit it's a vacuum leak. Down the road I'll replace it but for now it's fine. Just needed adjustment

 

Well done....

 

Thanks, back to the issue of the 02 sensor, replaced it with a good part from RockAuto (denso) and it still creates a check engine light. Now today I used an OBD2 to monitor the live stream of the sensors. Only two sensors were reading correctly while the others said N/A.

Here are those sensors indicated by the general Livestream
O2b2s1

02b2s2

02b3s1

02b4s1

02b4s2

​​​​​​All N/A, I'm starting to wonder if this is a fuse or relay. The only code the ecm puts out is p1646. If It's wiring does anyone have a diagram of the output wire. And if relay.. what relay should I check for p1646.




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Here's an update from today, so I tested all the relays in the passenger side bulk head. All prove to be working. I checked the passenger side fuse box, everything there is not blown, I did not check the actual fuse box relay.

I tested the new 02 sensor to see if the heater element was working. And... It was. I checked the previous sensor, it worked too. Then I check the original OEM one from 20 years ago, it doesn't work.

To add, I unplugged the sensor while the car ran, no change, it powers it but is not acting on communication. I even tested the power from the harness to the 02, it works. Ruling out power failure, relay failure, fuse failure.

Checked the wire, from the harness into the fire wall there is no damage. And I still can't get live data in OBD2, unless I'm not supposed to see it. When checking readiness systems it also gives a fail as all monitoring systems "are not active".

Honestly I'm about to just give up and deal with the bad gas milage. The fact that the restoration on the car has included a fair amount of blown modules like the chair, slm and abs makes me fear the engine control module isn't so clean either.

Any thoughts?

 

do you have an equivalence ratio and o2 current pid...i'm pretty sure the aj27 does. if you have a catastrophic vac leak you may be able to trip a false a\f sensor code as current flow is gonna pegged positive

please get a better scan tool

 

I'll try one of my different ones. We have a bunch. I just what was convenient (our garage is a mess). I'll reassess on Sunday with my 900$ tool for 2012 for 2010 and below. I'll update when I find the problem

 

A little update on the issue, so I used my good scan tool after rearranging my garage and finding it. And found this within the diagnostics.

Following this I also bench tested the 02 sensors and they both work, the heating element and the they both are transmitting data within the correct the limits. Yet readiness system stay incomplete. Does anyone have any idea would I should do next. Because I'm guessing I should just rip the ecu out and check for shortages at this point.

Here are the pictures from diagnostics. Didn't include the code but its still p1646, and what's the possibility its the downstream sensor sharing the same code?

 

The RH (Bank 1, Bank A) is the 'easier' upstream sensor on a Left Hand Drive XK8
P1646 refers to the upstream sensor on the RIGHT cataverter.(you are talking about the RH side of the engine?)

 

Yes the one on the passenger side (right side) for the LHD model. I've replaced that sensor 3 times with a denso OEM part and when it still didn't work I bench tested it. It was working perfectly. Both the heating element and it's data stream (tested with a. Meter).

 

Maybe I missed it. Have you done anything with the downstream sensors?

 

No I have not touched them. When I unplugged the problem sensor the code changes to low voltage, when I put it back in the same code returns.
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Hmm, I was not aware these upstream sensors could easily be tested. Just to be sure, have you checked the upstream sensors you are replacing a _wideband_ sensors, not lambda like the downstream? They work quite differently and are not interchangeable.

Best of luck, keep us posted.

 

Yes, it's the wideband, because they are expensive. According to RockAuto it's the right part and it was 225$.