'95 E420 - DM Codes 3, 4 & 25 - What to do next?

[Syntax26]

Anyone like to advise on my next step? What to replace/repair?

'95 E420 - 100,000 miles. Replaced engine wiring harness, ICM & spark plugs (Bosch F8 DC4) 5,000 miles ago - car was running great. CEL light came on - been pulling DM codes 3, 4 & 25 - erase them - they come back within few miles. Checked plugs and vacuum lines - all appear good. Cleaned MAP - same codes. Always runs 92 octane or higher.

Symptoms: Car runs great at mid-high RPM after accelerating. Car runs great idling in park. Problem is rough idle when in gear, brake on (such as at stop sign) AND upon accelerating from standing start or very low mph (10 mph or less).

Car still has original O2 sensors - but I'm hesitant to replace since not pulling codes for them.

Should I start with replacing knock sensors? (Code 25).

If lambda control is indicated (Code 3) - what do I actually replace/repair?

Any advice would be appreciated. THANKS!

By the way - I put a sport suspension in the car (springs, sway bar, shocks, brakes) and love it. Like a new car - so highly recommend anyone thinking about it.

[deanyel]

It sounds like you have pulled only the DM codes. You should build the code reader if you haven't already and pull all the codes. Lambda is the O2 sensor.

[JimF]

As deanyel recommended you need to pull codes from the EA, LH modules for sure. You can build the home-brew readed described in MENU#2. It's worth the effort.

Bosch specs O2 sensors for 60Kmiles so you could be due. Also don't forget the MAF sensor. . it might be contaminated, Menu#4a.

The rubber 'tips' of vacuum lines usually develop cracks which are not visible until you actually bend them a bit.

If Lambda is not functioning, I'd fix that first and that will probably fix the knock sensors.

[Syntax26]

DeanYel and Jim F....

Thanks for the very quick replies of advice.

I'll do the O2 sensors first (I should have known the lambda code is for the 02 sensors!)

And about the radio shack reader - would you believe I bought the parts and started to build it about 10 months ago? LOL! Life got, and always gets, busy...and I ended up putting the project aside.

By the way Jim - I've read your website a few times - that is where I learned about the MAF contamination and what educated me to buy the CRC cleaner last night.

So again, THANKS VERY MUCH for your time and advice. I appreciate it!

Jim V.

[JimF]

You're entirely welcome. . .

OK, now is the time to finish that 'project' . . . it's a handy tool.

Let us know what happens.

[Larry Delor]

Unless something changed between 94 and 95. you should just have 1 O2 sensor, and it is in a PITA location. Lifting the car up, and dropping part of the exhaust will be on the menu. (if I find the guy responsible for the location of said sensor, I will give him a swift kick in the rear)

[emerydc8]

The O2 sensor on my 1993 is really easy to change. I guess MB engineers discovered this and decided to redesign later models to make it much more difficult.

[deanyel]

I'm sure the 93s and 95s are the same. It's not a terribly difficult job if you have the right tool - a 22mm open offset socket, something like this - http://buy1.snapon.com/catalog/item.asp?P65=&tool=all&item_ID=74621&group_ID=1448&store=snapon-store&dir=catalog
I could see having to drop the exhaust if you didn't have one.

[Syntax26]

Guys...

Well I can confirm the '95 E420 O2 sensor location was designed by satan himself. Topside of the exhaust - vicinity of the "y" connection - pre-converter (naturally). The threaded bung is actually in a small recess - making it IMPOSSIBLE to get a wrench on. So you're forced to use a socket. Because of the wire - crow's foot socket! THE TOOL POPULATION GROWS AGAIN! ha ha!

Can also confirm - just one sensor (pre-cat) on this model.

Unfortunately...can't yet address whether the new sensor fixed the code issue - since soon as I got this done - I had to put brakes & shocks on the Landcruiser. (Snapped 2 caliper bolts - had to drill and tap threads in the steering knuckle - talk about PITA!)

Just wanted to say thanks for the help and advice - I'll chime in with "worthwhile" commentary on the diagnosis and fix when I get the car off the blocks tonight.

Jim

[Syntax26]

Dean, Jim & Larry,

Thanks for your input before...I do appreciate it.

As I mentioned when I started this post, I was pulling DM Codes 3, 4 & 25 on 8 pin connector (CEL on). I replaced fuel filter, spark plugs, distributors & caps, and 02 sensor. Cleared codes on 8 pin connector - drove car - codes came back in normal cycle.

Per your advice..next step was to finish building Jim F's home tester. I did so and pulled codes from X11/4 38 pin connector. Below is list (I include ALL operating pins - even if not seemingly relevant) (all code descriptions come from Baum manual):

Pin 4: Code 11 (Secondary air injection system, open or short circuit) - Cleared

Pin 6: Code 13 (Stop lamp switch) - Cleared

Pin 7: Code 5 (Stop lamp switch) - Cleared
Code 6 (Starter Lock-out/backup switch) - Cleared
Code 14 (Closed throttle position contact switch) – Cleared

Pin 8: Code 10 (Voltage Supply for LH-SFI control module interrupted or voltage supply for fuel injectors interrupted) - Cleared
Code 11 (Voltage supply for accessory equipment interrupted) – Cleared
Code 12 (Voltage supply for ABS, ABS/ASR or ASD control module interrupted) –Cleared

Pin 13: No Codes

Pin 14: Initially light lit continuously, but when checked AFTER finishing all other clearing – No Codes

Pin 16: No Codes

Pin 17: Code 5 (Knock sensors 1 and/or 2 faulty) – Cleared
Code 7 (Knock output switch in ignition control module faulty) – Cleared

Pin 19: Code 3 (Lambda control faulty) - Cleared
Code 4 (Air injection system faulty) - Cleared
Code 25 (Knock sensors faulty) – Cleared

Pin 30: Code 8 – wouldn’t initially clear – but when checked AFTER finishing all other clearing - No Codes

AFTER CLEARING ALL CODES - I DROVE CAR AND CEL CAME ON IN SAME CYCLE AS BEFORE (few miles driving - 3 ignition starts). Codes pulled from DM are same as before, to wit: 3, 4 & 25.

So.........any advice or guidance on where I should go next? I'm thinking knock sensor replacement and re-examination of ground wire connections .

By the way, I put in new engine wiring harness, plug wires and ICU about 5,000 miles ago and car ran well with no CEL over that time.

Also by the way - my experience level is such I can tear down and rebuild a Chevy small block (to the crank) and it works fine.

Also also by the way - these electronic issues with MB become somewhat addictive, don't they? I knew I was anal before...but I find myself reading everything I can find on how these controls operate. Yet - their just not straight forward like a good old chevy mouse.

Well, thanks for your time if you read all the way through.

Jim

[Larry Delor]

You can get a little closer to the wire in the MAF, by prying off the snap ring at the top of the MAF (utility knife worked for me) - the mesh then just lifts off.

I read that the wiring harness was replaced....but....what about the ETA (electronic throttle actuator aka throttle body to some)?

Just for grins, I would be tempted to check the fuses on the main module (in the module box - the box where you would think the battery ought to be) - that, and I would make sure the modules are nice and secure in their slots.

[emerydc8]

I read Jim's article and bought a can of that CRC MAF cleaner, which is still sitting in my garage--unused. I was under the impression that you had to take the MAF off the car to clean the hot wires. I guess it can be done on the car without any damage. Is the snap ring something that can be reused? Is the snap ring on the inside of the MAF at the edge of the screen?

[Larry Delor]

I took your pic, and zoomed in a little.
The arrow, points to the area of the snap ring that has the break in it. With a utility knife (or something similar) you can get underneath the ring, and gently pry the ring out. The ring will snap right back into place when you're ready to put it back.
After I used the cleaner, I waited a bit, to make sure that any solvents had time to dissipate.

[Syntax26]

Jim F & Larry,

Thanks for your posts.

Today I ordered the neutral switch and brake stop switch from Fastlane. We'll see what effect they have once I get them and install.

I'll check the module stability/connections per Larry's suggestion - and also the MAF screen removal technique to better clean the wire. I'd actually started this the other day...but upon starting to pry the large snap ring away from the collar, thought I might ruin something so I decided to stop.

As to the throttle actuator - I've read Jim F's dialoque on this and decided, in light of the cost, to defer evaluating/replacing this for the time being. In other words, take a look at the smaller, less expensive possible fixes first - leave the throttle actuator as an option of last resort.

But once I get 'er figured out, I'll be sure to let you guys know.

Jim

[JimF]

Originally Posted by Syntax26

Today I ordered the neutral switch and brake stop switch from Fastlane. We'll see what effect they have once I get them and install.

That's a good solution since the parts are not expensive and will cause a problem appear as if it's the ETA.

Originally Posted by Syntax26

I'll check the module stability/connections per Larry's suggestion - and also the MAF screen removal technique to better clean the wire. I'd actually started this the other day...but upon starting to pry the large snap ring away from the collar, thought I might ruin something so I decided to stop.

I would still recommend that you remove it . . . simply b/c you can really clean it better than you can on the car. The reason: wait until you try to start the car. . . nuff said.

Originally Posted by Syntax26

As to the throttle actuator - I've read Jim F's dialoque on this and decided, in light of the cost, to defer evaluating / replacing this for the time being. In other words, take a look at the smaller, less expensive possible fixes first - leave the throttle actuator as an option of last resort.

I think that is a wise course of action b/c you are not getting the codes that generally "infer" a bad ETA.