Just had some transmission work done and the CEL is on with a P1647 code and the reader says unable to determine severity. I cleared the code several times and it keeps coming back. The car runs well, but may be a bit sluggish perhaps.

It seems likely the sensor connectors may not have been reconnected properly when they replaced the exhaust. I checked Alldata but can't tell for certain where those connections are located - can anyone point me in the general direction? I know where the sensors themselves are and have read on this forum that this code points to the driver side upstream sensor.

I would like to check the connectors out myself before taking it in to be checked further.

Thanks -

 

I have located the connectors and there was a loose connection that clicked down when pressed - a larger black multi-plug just above the transmission. So far the CEL is not coming on in about 15 miles of driving so that may have been the reason for the P1647 code.

 

Wrong. It came back on when I restarted the car. Still think it is a connection but will need to dig deeper. Since it only comes on at startup, perhaps the computer can't find the sensor when it does a status check?

The picture of the sensor connectors in AllDataDIY doesn't really look like anything I am seeing down there, but I will have more time to spend on it this weekend. If I am not even in the right area, feel free to chime in... Are the sensor connectors accessible from above or below? AlldataDIY describes them as on the engine mounting bracket...

 

IIRC from my '99 Sovvy they are on a mounting bracket on top of the trans. Mine hadn't been replaced properly. The upstream ones are heated wideband and if the heater goes (black twisted pair, approx 6-8 ohms) it will throw a P1647 or P1646 error. If the heater has gone, replacement is the only cure.

Before that though, if you had work done, check that the upstream sensors are connected to the upstream cables and if they are that they haven't crossed left and right banks. They are awkward to get at but I could only see getting to them from on top. A ramp might show a different view but I don't have one.

Jim

 

Thanks Jim. I have 2 light blue and 2 black multiplugs that must go to the 4 sensors and a larger plug that were likely all clipped to the bracket at one time, but now only the large plug is on the bracket and the rest are floating free. I can't tell if the sides are switched (perhaps the wire colors would tell me that), but everything is securely snapped together. I pulled them apart and re-connected them to make sure.

Anyway, with the code cleared I took a short drive, shut her off, and the code returned after starting back up. The reader shows 3 codes: P1000; P1647 Severity Unknown, Contact Service Group; and a plain P1647.

If I swapped the upstream plugs and threw a 1646, would that confirm I have a bad left side sensor? I would have to verify I have right to right and left to left to begin with... can that be verified by wire color?

I am still having trouble believing the sensors went bad at the same time I had the transmission work done. Makes me think it must be a connection somewhere. I am admittedly not confident about the taking her back to the tranny shop for the sensor code issue, but perhaps I should let them try to fix it.

 

I have found diagnostic information on troubleshooting the O2 sensors but need a diagram of the pin outs on the connectors. AlldataDIY doesn't seem to have it. There are a number of checks I could run if I knew what pins where what.

Anyone know what the pins and/or wire colors are on the upstream connectors?

 

OK, I found the 2001 Electrical Guide for the XJ and it answers many of my questions. The upstream connectors are grey (I called them light blue) and I know which wire colors are for the A or B banks. I am still trying to figure out what the wire colors (pin out) relate to so I can run the tests.

 

The 4 wire upstream sensors are heated. The sensor incorporates a heater to bring it up to temperature when you first start the car. Older sensors used the heat of the exhaust to warm them - this did not allow accurate emission control when the car was started from cold. When the heater of the O2 fails you get a code but the car often operates normally since the actual sensor is still working. The is a common failure - and it very likely that this is the problem. Normally the heater loop is open when you test the pins on a failed sensor -- but they can be sneaky.

The sensor connection block is a little difficult to get to -- maybe the previous owner/ mechanic removed the block to get to and disconnect the sensors (even though it is not necessary) and then failed to take the time to properly finish the job. The sensor wires are also routed under a heat shield and held in place with "zip" ties

Amazon normally has great prices on the O2 sensors. I purchased one (4 wire) along with the proper tool for less than $100.00. Make sure to order the correct direct fit sensor -- don't use a generic. I would order a new sensor and connect it to one of the two free connections and see what codes still remain -- this will give you the left and right socket.

The left side sensor is a bit difficult to remove - not much room.

Good luck

 

Thanks yeldogt- I have figured out the connectors thanks to the Jaguar 2001 XJ8 Series Electrical Guide (which I will try to get added to the sticky if its not there already), but like you say they can be tricky to properly diagnose and if I have to go in to look for a damaged wire or whatever else it might be I might as well change both of them out. I have been to the B bank upstream connector when I rebuilt my heads so I know what I am in for. I want to get all the connectors back on the block and one connector has a broken clip lock that should be secured.

I'll need to make sure I get the right sensors, but sounds like I can wrap it all up with a bow for under $200. Sold.

 

Last weekend, when I did an inspection of my O2 connections I also did a hard reset. Because the car was running well despite the code, I wanted to make sure the code wasn't anomalous following my transmission repair.

After the hard reset it has been running worse than before, very sluggish and slow to accelerate. I still have the 1647 code and CEL, but now my ABS/Trac light has gone away! Actually it comes and goes, but for the last several starts it has stayed off. Go figure.

Anyway, I am wondering if poor performance is normal behavior with a bad O2 sensor. Two new sensors are on the way, so this weekend I will swap them out. Hopefully the usual performance will return.

Should a hard reset follow replacing the sensors or just let the drive cycle do its thing? Should I disconnect the battery when doing the job?

 

Can anyone shed any light on this situation… I have a 2000 XJR & I keep getting a P1646.This is the only code. I have over the past year replaced all of the O2 sensors & knock sensors. The check engine light will not go off. We have tried swiping out computers & sensors from other like cars and it still will not go off. Once reset, it will stay off for a while then after 1-2 starts, it comes back on. We’ve also tried disconnecting the battery as well. I’m at a loss…..

Please share your thoughts.

 

Miamixjr,
My guess would be a bad wire or connection somewhere between the connector and the ECM. You might try checking resistance from the O2 connector and the ECM connector to see if if any of the wires are bad.
Good Luck!

 

Jaginblack, I am in the same situation you where in. Strange that I just had my transmission rebuilt & code P1647 come up right after i got out the shop. My first thought was somebody didn't connect the wires correctly, so i doubled checked my self and everything seems to be plugged in correctly. My light is is still on and comes back on if I erase using a scan tool.
Did the new sensor you order fix the problem?

 

2001 JX8 4.0. With a hard P1647 code (upstream sensor driver side (USA)) Can this sensor be accessed with more ease while up on a lift for the replacement, or is having the car on the deck and removing the expansion tank and heat shield the only option? I believe it's only the heater portion as the car runs fine, but is also indicating Restricted Performance at times. Can anyone recommend the best replacement type, I'm considering Denso. Does anyone have the correct part number, as when I start this job, I want to verify the correct part before ordering. I always try to "Do it once, do it right"