I have just gotten the CEL on and did a check for the fault code but no message and did a fault code check.

It came up with P1646. I erased it, but it comes up again after the next drive, so it seems valid.

The JTIS tells me this:

EOBD
P1646

FAULT DESCRIPTION
EOBD Fuel pump 2 (SC) relay malfunction

MONITORING CONDITIONS
Ignition ON > 5 seconds


DEFAULT ACTION
When fault is detected, ECM:
– Limits engine speed to
3000 rpm

POSSIBLE CAUSES
Fuel pump relay 2 failure
Fuel pump relay 2 to ECM circuit fault
Fuel pump relay 2 coil power supply open circuit
ECM ground circuit fault (relay coil drive

This is about where my knowledge stops and I need a bit of help to continue so that I can fix this.

Is it as simple as changing the Fuel pump relay or what do I need to do?

The car runs pretty OK, but it sometimes feels as if the engine is running a bit rough. Mostly on longer drives.

Thank a lot in advance

Thomas

 

Might try swapping the fuel pump relay with another. Most are the same.

Been a lot of SC fuel pumps failing this Winter but there is really no sensor code for that.

 

I think you may have the wrong code definition there. P1646 on AJ27 '99 on is "ECM HO2S control malfunction – B bank, upstream". You have a possible defective pre-cat O2 sensor is all. P1646 as a fuel pump relay error is from older (e.g. '95) regular XJ - suggest you check your JTIS again.

Jim

 

Good catch!

 

Mebbe not - need to know the VIN to be certain as very late models had the fuel pump code as P1646 again so my error perhaps. Can the OP confirm?

Jim

 

Hi guys

The Vi No. is: SAJAC14MX1LF36716‏

Hope that helps clarify things...

 

BTW: I looked in the boot to check the Fuel Pump 2 relay, and there was none there!

I put Auxiliary positive relay in its place and reset the system and went for a couple of drives.

On the 2nd one, the P1646 and CEL came up again.

 

It sounds like your car is not supercharged. That would be why you do not have the fuel pump 2 relay. That code is a problem as someone else mentioned. They used it for 2 totally different things, fuel pump fault and O2 sensor fault. If your car is not supercharged I would check the fuse and relay for the O2 heater circuit. If the fuse and relay check ok check for 12 volts and ground at the O2 sensor connectors heater wires. If you have power and ground you could replace the bank 1 sensor as a guess without further diagnosis but they are expensive. Proper diagnosis would require monitoring the O2 sensor output on a fast volt meter or oscilloscope.

 

Yes it does, definitely the Fuel Pump 2 Relay message. My error, not O2 sensors at all (I'm sensitive to them as both mine had to be replaced and P1646/P1647 is burned into my brain). Wish they wouldn't keep re-using the codes for other things on later models. Hey ho!

It is down as a CK2 which means it needs the error on 2 consecutive trips before it will throw a CEL and a P1646. Is the (SC) reference in the message to "SuperCharged" - can someone confirm?

Jim

Stop press: just read Real_Tech's post - if you have a sniff of a suspicion it might be O2 sensor related after all, swap over the left and right bank sensors if the wires will reach - the P1646 will change to a P1647 if it is O2 sensors.

 

Jima:
As I read the JTIS, 5 digit VINs preceded by F use this code as wideband O2 sensor.

 

Jims idea is a good one but there is an even easier way to check the sensor. After verifying you have the proper heater power and ground you can swap the harness connectors behind the throttle body mounted to a bracket on top of the trans. Bank to bank the connectors are the same and will easily reach. Just make sure you test the power and ground first as without those the code will change banks even if the sensors are good. Don't forget to switch the connectors back after testing or you will cause all sorts of trouble as the ECM will think the bank 2 readings are from bank 1 and alter fuel trim accordingly. This last part is a fairly common mixup on engine swaps and what happens is that one bank will be driven full rich and the other full lean.

 

Hi Ross, that's what I thought and the symptoms are exactly right however according to my JTIS (v1.3) for AJ27 MY 2001-on from VIN F20645 onwards P1646 refers to the fuel pump. This is very odd - I'd like to get to the bottom of this as I want to be able to trust my JTIS. Any further thoughts?

Jim

 

yep. I dunno. The wideband sensors theoretically happened in '99, I believe. I don't have access to the parts list, so I am not sure.
WILD GUESSES??- Wrong data in JTIS, replaced ecu?
Since it is NA, AND it did noit have the pump2 relay, I would have to believe it is certainly not a fuel pump problem. AS yiu said, sure wish they didn't reuse codes.