If you see values changing no need to test wires. Atached are some pages that describe what is going on with the O2 sensors. Basically they see normal changes between certain ranges. Rock steady or zero voltages are bad. The ECU does lots of math to compute if the catalysts still meet federal standards, and determine the proper fuel mix.

 

code 1668 has to do with wiring being disturbed between ECU and BCU, for immobilization system.. this has the possibility to prevent engine from running very long or even cranking.

The 300 level codes are misfires.

The other codes are detailed on these two pages from the ECU manual by Bosch.

 

Thanks Buzz.
So i hooked up my new scanner to my mazda P5 on the way to work today and now I see how things should be cycling. The O2s in the Disco are not cycling so I have some work to do.
I'm not so good with electrics so any tips on testing procedure would be gratefully recieved.
Jon.

 

Could low octane fuel be an issue here?
When I first found the car the tank was so dry it wouldn't start since then it has had only 87 octane fuel. After going through the owners and RAVE manuels today I see they specify premium fuel only.

 

Today is a holiday here so I will be going through the o2 wiring. I'll try to keep a running log of my actions and results within this post to keep everything in one place.
Feel free to comment or point out my idiocy as I go.

Step 1. Tested voltages at all harness o2 plugs: key off no power anywhere, key pos.1 pin2 shows 0.01V on all plugs, key pos.2 pin 2 shows 0.44 on all plugs, pin 3 shows BattV on all plugs


Ok, I've gone through everything and can't find a single problem. The only thing I'm not sure on is the 0.44 volts showing on pin 2 when the key is in pos.2. I must say that the wiring in this car is like brand new, no signs of Mr.Hack or Senoir Slash any where.
Gonna have a beer then fire it.

 

Codes have returned. I'm stumped, any ideas?

 

More beer?

 

Already thought of that...several times, it's the only thing stopping my brain from hurting!

 

Well I had to take a break from this issue after an altercation with a Jeep Cherokee. The disco needed a new front clip but the Jeep ended up in the scrap yard so I guess you could say I won.

As of right now I have done the following:

Tested all wiring in the o2 harness, no shorts of any kind.
Checked wiring at the T under the hood
Cleaned and checked o2 plugs, no bent or missing pins
All o2 sensors are new
MAF is clean and cycling
IAC has been cleaned but has a pretty good hum to it
Checked all fuses
Checked cycling of upstream o2's from cold start. They both cycle for a few minutes then drop to a steady 0.44 volts shortly followed by codes and MIL.

Codes are: p0134. P0154. P0135. P0155. P0141. P0161. P0160. P0140

I'm on the verge of taking it into my LR dealer to have the computer re-programmed but if anyone has any ideas I would like to try them before I do.

 

I think I may have found something. Inbetween the fuse box and fire wall theremis a large grey connector plug. Upon taking this apart i found that the one pin that is by its self in the group has obviously become discoloured with heat and is surrounded by melted plastic.

This wire is brown and pink and shares continuity with the same colour wires on the o2s and fuse no.2. Am I on the right track here?