W164 ML320 05 CEL P1402 Code Limp Mode

[dnamlot]

I have an ML 320 W164 05 model with 126K, auto. I love the car but there has been an intermittent limp mode fault that has now been joined by a check engine light and a P1402 code. The problems in order of there occurrence are as follows and this is what I have tried based on the advice of forums such as these.

Faults

1. The car starts fine, most mornings in full power mode. No matter how long the journey 5 mins or two hours it remains in full power throughout the journey. No matter how short the interval is between engine switch off and the second start it enters limp mode. Weather/temp makes no difference. The car can be stone cold or warm and it still starts in limp mode. The car drives fine through the autogears limiting around 2,000 RPM but is gutless compared to full mode.

2. For a couple of weeks we had an intermittent Check Engine Light that was then associated with the limp mode but now it is on permanently in and out of limp mode.

3. I bought a WIFI OBDII reader to use with an iphone (understanding this will only provide limited info), the only code is P1402 which if cleared does not take the car out of limp mode and returns with the CEL after 2-3 starts.

Action Taken

1. Following advice on other forums I cleaned the EGR valve which was not overly dirty. At the same time I replaced the air and fuel filters.

2. Lots of forums suggested P1402 and the limp mode could be fixed by replacing the DPF Sensor. I did this with an OEM part for £22 delivered. Sadly the CEL, P1402 and limp mode remain.

I suspect I am destined for a date with a STAR computer but before I do does anyone have any advice or ideas on anything I should try? Are there any other related sensors or checks I could do related to the P1402?

Many many thanks for your help in advance. David

 

[HITECH]

P1402 limp mode hassle

Hi this year i worked on my m8ts 220cdi and few other cars with the same fault.What i found with this fault was the DPF sensor had gone faulty. You can clean out ur EGR valve til the cows come home and go round in circles with this fault but this P1402 points to the DPF sensor. It is located at the back of the air filter box. Bolted onto a heatsink. What i have found is it gets loose from the heatsink and wobbles about with the airfilter box. It has to be tight against the plate as its attached to as the plate absorbs and takes the heat out of it. Ive seen 4 of these sensors overheat on 4 different cars this year resulting in P1402. My first experience with this fault was with a m8ts car and eventually sourced the fault which was a bit of a head scratcher. You will get told REPLACE THE EGR, REPLACE THE MAF, REPLACE THIS REPLACE THAT but a lot of people on the forums im seeing spend a lot of money trying to get it sorted and took their car home from the garage with the same fault. Your check engine light will go on and off randomely with this fault aswell as when it cuts off the turbo and goes into limp mode theres a slight error kicked up with the actual EGR system P1405 or a fuel error code. They are most defenetly false positives. Hope you got this fixed without spending too much money on it. Ive known people to get the catalytic convertors replaced DPF's etc etc have the code force cleared on a star machine only for it to return back a few days or months later and back to square one. Guys in here helped me with the location of the sensor. Great bunch of guys with a lot more knowledge than i have on mercs but this fault was a head scratcher and i sourced it myself. A CHEAPO DPF SENSOR WILL MOST LIKELY KICK BACK A P1402. Get a proper mercedes sensor. Ive replaced maf sensors and dpf sensors with cheapo ones and the original fault remained or new fault codes appeared. Also check the wiring to your EGR solenoid connector.

 

[dnamlot]

HITECH - you are a star. I searched for the original Merc DPF sensor and most retailed at £59 I found one for £35 on ebay. I removed the OEM sensor that I had paid £22 for and made no difference. With the Mercedes DPF sensor installed I have my car back to life. What a difference, code cleared and 10 trips later it has not returned. All assume that this has resolved the issue I will post again if it has not. Thanks to all that contribute to successes like this on this site.

 

[HITECH]

if you have not put any heatsink paste onto the gold metal part of the sensor. the part that the screw goes throw and bolts it to the bracket. do so. it will make the sensor last much longer and it wont heat up so much. Its defo worth the few minutes of ur time to pop the bonnet up and do this for all the time it takes. Any computer cpu heatsink paste ( can get it at any computer shop) will do as u only need to smear it over the sensor at the part it is tightened up against the bracket. Also keep checking maybe once a month that its still securely tightened and not loosened off as with the heat and engine idling it does happen. Glad ur sorted m8.

 

[Cheylint93]

So my car does the exact thing as the original poster. However mines not a diesel. Any idea on what I can do to solve this problem?