I have a 2001 XKR coupe, and recently had the check engine light with codes P1646 and P1642. I clear them and the P1646 always comes back, and the P1642 comes back only sometimes. Car runs fine with no other messages such as restricted performance, etc. Doing research, it appears that P1646 relates to the 2nd fuel pump relay on my XKR. I switched out the relay with another one, and the same P1646 code came back, so I assume that rules out a bad relay. What else can I try to correct this engine light? The fuel pumps were changed out about 5 years ago.

 

I believe P1646 is for the upper oxygen sensor on the passenger side.

 

I think he is right on the 02, recheck that code

 

Hi.

Very confusing.

From JTIS Code P1646

VIN 001036-018108 no such code
VIN 018109-031303 Fuel pump 2
VIN 031304-A00083 Heated O2 sensor
VIN A00084-A11140 Heated O2 sensor
VIN A11141-A30645 Fuel pump 2
VIN A30646- and on Heated O2 sensor

 

It is confusing. So since I have a 2001 XKR, and my VIN says it should be a "fuel pump 2", I'm leaning towards that instead of the 02 sensor, what can I do to try and sort out this engine light?

 

In case you can get to the (upstream) O2s easily (as on my car) then you could test the heater ohms (about 1) as usually they blow open circuit. On my car (sorry, it's all I have!) it's easy to unplug the sensor and do the test.

If both sensors are good I suppose it must be a fuel pump!

 

Well if you think its the fuel pump you need to change it, but most faulty fuel pumps show very different symptoms and don't throw codes pointing to the fuel pump. Note the 1646 indicates RELAY not fuel pump, as well as a 1642 indicates a intermitant CAN error it's more likely a sensing / elec problem than a fuel pump.
See post 12 here