Cooling fan running permanently on Mercedes A150 (W169)
After a small accident with my A-Klasse (W169), the people in the dealer services replaced the radiator. A few weeks later the cooling fan started working permanently in "turbo mode". This resulted in the difficult warming up of the engine and the complete discharge of the battery. After another visit to the dealer, the problem was solved.
A few months later, during the summer period, I saw a few times the indicator for engine overheating on the board. One day decided to take a look and I realized that the cooling fan is not operational. A quick check revealed that the guys from the dealer service "fixed" the problem by cutting the power line to the fan control module. After restoring the power line, the fan started to spin permanently again. Since this was after the warranty period, and impossible to prove who cut the cable, I asked them about fix and they give me an offer for approx 2000.00 Eur, and I decided to leave it like this for the moment. After almost a year the fan gave some defects and become noisy and producing vibration in the car front. Spending a few hours disassembling the fan holder I found that there is a crack in the rotor, which was resulting in dis-balancing it -> vibrations. I fixed it and the fan became silent again, but still going in "turbo" mode.
For a period I was searching any kind of information about this problem and found multiple posts, related to fan control unit defects, disconnected data lines, engine coolant sensors, etc. Going after any of these cases resulted in nothing.
Week ago, by incidence, I saw the following post: https://au.autologic.com/news/engine-cooling-fan-running-at-constant-high-speed . This description sounded reasonable, so I decided to give it a go. I have iCarsoft V1.0 tester which I used to check the parameters from the post. The results were:
- at engine start (fan is still):
- a few seconds later (fan spinning):
- a minute later (fan spinning):
- A/C refrigerant pressure:
From the last test, I concluded that the problem is in the A/C refrigerant pressure sensor (A 211 000 02 83). I found in the Mercedes documentation the location of the sensor and was able to access it from under the front. So I found that actually, the connector is out - the sensor is disconnected. It was not possible to connect it by unknown reason, so was necessary to access it, following procedure from document AR83.30-P-5430AK, step 3.1 only - removing front bumper (described in document AR88.20-P-2000AK).
After the front bumper was removed, I was able to access the sensor, as shown here:
The connector was no possible to be inserted completely which makes a necessary part of the ribbon sealant from the 'female' connector to be cut and taken away. Then the connector entered completely and locked into position.
I ran all the tests again, and got these results (this time the refrigerant pressure was indicated and it was approx 6Bar):
- at engine start (fan is still):
- A/C is on for 10-15 sec (fan spinning fast):
- A/C is off for about a minute (fan spinning slow):
- a few minutes later (fan is off):
- after a while, when the engine temperature is around 100 centigrades (fan spinning slow):
- after a few minutes, the engine temperature is lower (fan is off):
This is how I succeeded in resolving this painful issue, which was going to generate a lot of expenses only because the people in the dealer service did not finish their job :(
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