Land Rover Repair: 2003 Landrover Discovery O2 sensor problems..., closed loop control, failure modes

Question
I keep getting a O2 sensor code and engine light.  I have spent a ton of money having the dealership trouble shoot and am getting very frustrated.  We have replaced catilic converters, the 02 sensors, mass intake sensor, wire harness, and have dumped thousands of dollars into this problem and the dealerships seem to be clueless.  Any ideas on what my still need to be checked???  I am now desprate and tired of throwing money down the drain for an engine light.

Answer
Hi Brian,

sorry to read that you are being yanked around by the dealership.  I hope you are being compensated by the dealership for their inability to solve this problem.  If you complain loud enough, you may be able to recoup some of the cost of 'teaching' them how to repair '03 Disco's.

I recently saw a problem that looks much like yours.  It was with a '01 Disco and he too was getting 02 sensor failure codes.  Turns out that the sensors were not installed properly.

Here are some other possible causes:

Here's the possibilities:

Failure of the closed loop control of the exhaust emission system may be attributable to one of the failure modes indicated below:

1. Mechanical fitting & integrity of the sensor.
2. Sensor open circuit / disconnected.
3. Short circuit to vehicle supply or ground.
4. Lambda ratio outside operating band.
5. Crossed sensors.
6. Contamination from leaded fuel or other sources.
7. Change in sensor characteristic.
8. Harness damage.
9. Air leak into exhaust system (cracked pipe / weld or loose fixings).


I hope this helps.  If you know what codes are being triggered, send them along and I'll try to help.

Best of luck,

JohnMc