Hello fellow LR3 / Discovery 3 owners.I'm trying to troubleshoot a P0296-00 code "Post Catalyst Fuel Trim System Too Lean Bank 1". This is on my 07 LR3 4.4L HSE.

When the check engine light first came on, I noticed no change in performance but now the car seems to struggle to get up to speed from a stop but is fine once it gets going. The fan sounds a bit loud when taking off from a complete stop. I've replaced the fan and relay already, and my voltages are 14.5V while vehicle is running so I think the alternator is good. This seems to happen only when acelerating from a stop as well. but then it eventually seems to settle down.


So far, these are the things that I have tried which have not worked:

• Cleaned MAF sensor
• Swaped positions of the down stream O2 sensors between bank 1 and bank 2. Same results. Both sensors were Denso brand.
• Replaced cracked air intake hose / box
• Checked for vacuum leaks in engine bay with carb cleaner.

• I measured the exhaust temperatures with a temperature gun before and after the catalytic converter. My readings were about 400F before and about 450F after which seems fine based on what I've read.
• Attempted to tightened O2 sensor on bank 1 sensor 1 as it appeared there were bubbles around the connection when sprayed with soapy water. (It was difficult to tell if I actually moved the sensor at all in the awkward position I was in.)
• Sprayed the rest of the exhaust before and after catalytic converter to check for leaks
• Drove vehicle and monitored bank 1&2 sensor 2 and short term and long term fuel trims

While idling, my long term fuel trims are around 6% but once I give it any throttle, they shoot up to 11 -13%. Sometimes as high as 16%. I've attached a screen shot from my GAP tool of the short and long term fuel trims overlaid.
I reset the codes and took the vehicle on a longer drive at higher speeds to see if long term fuel trims would eventually drop and lower the average but they did not. Costing around 75 mph, the long term fuel trims were around 8% but again, as soon as I give the vehicle any throttle, they shoot back up to 13% +.

There were some odd readings on my 02 sensors that I captured below. This happens pretty freuently where both 02 sensors will drop to 0V for a few seconds and then return to fluctuating values. They tend to hover around their higher limit aroud 0.8V - 0.9V most of the time rather than around the middle of the voltage band. I'm not sure if there is an electrical issue in the harness that could be causeing the sensors to momentarily drop out like that.

In my GAP tool, there are also short term fuel trim sensors that I can read and they give very strange values. They go between-0.781% to 0% constantly. There are no values in between. I'm not sure what this fuel trim sensor even is because I thought fuel trim was based on combinded readings from the MAF and O2 sensors to determine appropriate fuel trim.

The previous owner also said he chaned the O2 sensors, but I'm not sure when. This makaes me think it's not bad O2 sensors, but not 100% sure.









If anyone has any suggestions based on the screen shots provided, or other data I should collect with the GAP tool to help with diagnosing the issue, that would be be awesome.

Cheers