MK3 LS400 Intermittent Check Engine Light

Byngo123 · June 20, 2022

Couldn't find another post that related to the issues I am having, so I have created a new topic, please feel free to let me know if I'm just echoing someone else!

I have a 1997 LS400 on 84K miles. In relatively good nick, no obvious issues. I've owned this for around 2 months now, and I've not had any problems with it other than a check engine light that comes and goes as it feels like it. I can be driving to work and it will pop on, no loss of power or strange noises, the car will drive as it normally does. I will stop the car and restart it, the light will turn off, however it seems to randomly come back on at any time. Obviously I want to address this issue before it potentially becomes something serious.

Has anyone else had this issue with their LS? I haven't checked codes yet, but I thought I would ask and see if this has happened to anyone else before I start diagnosing potential issues.

steve2006 · June 20, 2022

Hi James,

You need to get those codes read as it could be a multitude of things, personally given the age and mileage of the car my money would be on the O2 sensor or exhaust related problem like a blowing Y section or EGR pipe but this is pure speculation.

Get the codes and come back with them.

BTW I notice your fuel gauge shows full, is this also faulty as £50.00 doesn’t even get me half a tank these days 😀

Malc · June 20, 2022

James hi, it's good to see your speedo and rev counter working tho' ... at 25 years young mine did too mostly ...... electronics have a way of telling you they're just getting a bit tired sadly :unsure:

BUT back to your Q .. never seen that appear on mine yet

Good luck finding it tho .... you have done the obvious like checking the engine oil levels etc ?

Malc

Byngo123 · August 1, 2022

On 6/20/2022 at 9:49 AM, steve2006 said:

Hi James,

You need to get those codes read as it could be a multitude of things, personally given the age and mileage of the car my money would be on the O2 sensor or exhaust related problem like a blowing Y section or EGR pipe but this is pure speculation.

Get the codes and come back with them.

BTW I notice your fuel gauge shows full, is this also faulty as £50.00 doesn’t even get me half a tank these days 😀

So I've pulled the codes last week, haven't really had a chance to look until now, but I'm getting the following.

21 - Main oxygen sensor signal (on left bank)

52 - No. 1 knock sensor signal

71 - EGR system malfunction

I drove it this morning and it did have a bit of a stutter around 2k RPMs, then proceeded to throw up the CEL again. Pulled over and gave it a restart, code vanished and drove fine all the way to work!

After doing a fair amount of research this morning, it looks like the 52 code for knock sensor can be caused by a multitude of things not related to just the actual knock sensor, including the O2 sensor and EGR causing rough running!

Any advice on first steps? I've got 2 O2 sensors on order, might as well get both replaced at the same time for peace of mind, but will want to address the EGR system sharp-ish to avoid any further issues. What a headache!

Malc · August 1, 2022

James, notwithstanding all your codes stuff just tell us how it is now:

is she driving well with good accelleration and power in PWR mode especially ?

Has she had a good hard blow-out along the motorway, uphills too ?

Is she performing well generally ?

Malc

Byngo123 · August 1, 2022

10 minutes ago, Malc said:

James, notwithstanding all your codes stuff just tell us how it is now:

is she driving well with good accelleration and power in PWR mode especially ?

Has she had a good hard blow-out along the motorway, uphills too ?

Is she performing well generally ?

Malc

Hi Malc,

Seems to be fine. I've been driving it almost daily for 3 months, seems to run well until that light comes on, and then it seems a little sluggish and jerky until I turn it off and on again!

All fluid levels are good and there's plenty of it. Average MPG seems to be between 20-25 from what I'm calculating a full tank is getting me (380 miles to roughly 70L).

Most of my journeys tend to be on longer stretches of road so it will get a good blow-out when I can, but there is the odd short trip to the shop thrown in. But I guess the short version is that it's generally a good runner until I get the light on.

Malc · August 1, 2022

3 hours ago, Byngo123 said:

(380 miles to roughly 70L).

it's actually 80.1 ltrs tank and i find there's about 100 miles left in her when the orange light pops on

Malc

Stanwithaplan · January 25, 2023

My engine management light has been off for a week now (which whilst not being very long, is a new personal record), after finding a hole in pipe that runs from the air intake. Picture of pipe attached but not the hole, sorry.