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SOLVED: Replacing the thermostat fixed my issue! It's a very easy job on the M276
Hello all!
So I took my car to a repair shop to have my radiator and coolant temperature sensor replaced a few weeks ago. I had a coolant leak. Since then, the car has been great. However, when I was on the way home from school today, the radiator fan started to run high. It sounded like a jet engine. A little yellow temperature icon also appeared on the gauge cluster(similar to this but yellow: https://www.benzworld.org/threads/wh...069898&slide=0). Has anyone encountered a similar issue?
I plugged in my scan tool and monitored the car on my way home. There's no CEL but I got a P0692 "Fan 1 Control Circuit High".
It's so weird. There are no leaks of any kind anywhere. The car was not overheating even before the fans kicked in. When the temperature reaches around 210 degrees F, that's when the fan goes into maximum overdrive and stays on. I was actively monitoring the coolant temperature via the scanner and it stayed around 180 degrees F when the fans were running. I checked fuse 22 in the fuse box and it looks good. The heat was working perfectly fine too. This issue only happens when the car reaches the operating temperature then the fans kick in. When the ECO start/stop kicks in, the fan will die down and stop until I get moving again. When I shut off the car, the fan will continue to run for about a minute or so and then it stops.
Could this be the thermostat going bad or perhaps even my serpentine belt? Maybe even the coolant temperature sensor? I want to replace the fan but I don't just want to throw parts at it. I would appreciate any advice!
When radiator got replaced, that means the connector of the cooling fan needed to be disconnected.
So maybe the small wires or its pin, did not sit well. "Fan 1 Control Circuit High" would mean the PWM signal sent to the fan is LOST or at 90%. LOST of signal, the fan will go top speed as precaution.
Since you said that the coolant temperature is okey and not overheating, I suppose the air bubbles removal was done well.
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This is the connector
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Last edited by S-Prihadi; Dec 13, 2023 at 04:49 AM.
If pin 3 at the connector, the red-green or Black-Red 1 mm or 0.75mm depending on which engine variant or option code, for my M276 3.0 Turbo it is the RED-GREEN..... if this wire connection is lost, or bad contact,
the 10% PWM signal as FAN STOP is also lost and fan go for top speed. Fan stop is not 0%, for safety reason when wire get accidentally disconnected or cut or whatnot.
Use Duty Cyle capable DMM to see the PWM signal duty cycle.
If pin 3 at the connector, the red-green or Black-Red 1 mm or 0.75mm depending on which engine variant or option code, for my M276 3.0 Turbo it is the RED-GREEN..... if this wire connection is lost, or bad contact,
the 10% PWM signal as FAN STOP is also lost and fan go for top speed. Fan stop is not 0%, for safety reason when wire get accidentally disconnected or cut or whatnot.
Use Duty Cyle capable DMM to see the PWM signal duty cycle.
Thank you for the valuable information! I unplugged and replugged the cable but the issue still arose. I will look into getting a digital multimeter. I’m not exactly an expert in electric work so what type of values should I be getting when testing the connector?
10% = FAN STOP
90% = FAN MAXIMUM
0% = error, fan go MAXIMUM
100% = will be error too I believe, fan go to MAXIMUM
The guy in the video uses regular voltage setting and not duty cycle, so 10% of 12.7V = 1.27V, something like that. So 50% is 50% x 12.7V = 6.35V ( assuming decent power supply is connected to battery )
This fan can suck easy 80 amps, so if no power supply to assist, battery voltage can drop to 11.5V or lower
Last edited by S-Prihadi; Dec 13, 2023 at 10:06 AM.
it is impossible to read PWM signal with a basic AC/DC DVM.
Fan output is not DC voltage and not a 60Hz AC sinusoidal voltage.... cheap DVM has no accuracy outside of it's range of measures.
Only a more advanced DVM with frequency counter and PWM duty cycle measure can be used.
Simple bush-fixings...
It is totally possible to troubleshoot the fan control without PWM accuracy. As long as we know basic DVM is lying blindly: we do NOT rely on it.
The fan speed already tells us what's happening!!
It's like trying to measure the outdoor temperature with an roasting oven temperature gauge: useless range.
Above YT video shows that newer cars:
-- the fan LIN does not come from the ECU directly. ECU request fan speed via CAN-C to an intermediate module.
-- At least now the Fan control uses a classic serial LIN instead of the legacy PWM signaling we are accustomed to.
Last edited by CaliBenzDriver; Dec 13, 2023 at 05:22 PM.
aha.....so newer car has broker module to control fan and not ECM/ECU direct like ours... I glanced at the video only based on title
Thanks Cali
Ok so I finally got around to changing the entire cooling fan. I cleared the code after the repair. The car was running perfectly fine after 24 hours of changing it out.I took it on the highway, had it in stop and go traffic. Nothing wrong. The car would reach operating temps and everything was perfect as it can be.
However, on my way home tonight, I was driving on the highway when I saw that coolant light on again. The fans kicked into high gear again too. I got home, turned off the car, and it took a good 5 minutes for the fan stop running on high. When I opened the door to exit the car, it kicked into high gear again and stopped after about a minute.
I don’t understand. Is it the ECU? Based on what you both were discussing, there appears to be something else that’s acting funky. How can I test the prefuse located by the battery?
You do not need to test the F32 prefuse if the fan CAN RUN. If that big size prefuse blown, your fan CANT RUN at all.
Your coolant light warning is low coolant or hot coolant ?
You may still have air bubbles not completely cleared from your cooling system.
You do not need to test the F32 prefuse if the fan CAN RUN. If that big size prefuse blown, your fan CANT RUN at all.
Your coolant light warning is low coolant or hot coolant ?
You may still have air bubbles not completely cleared from your cooling system.
It was this symbol in the center gauge cluster. Coolant levels are good. I don’t see any leaks. Temperatures were hovering at 170-175 degrees F.
How would one go about clearing the air in the system? I opened the coolant reservoir cap and squeezed on the radiator hoses.
SUPPOSEDLY : That yellow thermo is low coolant level...hhhmm, mine is a complete TEXT BASED warning, so no guessing.
Read ur user manual will be best.
Maybe your coolant level probes are loose for its connection or crusty already.
You are using MB coolant right ? If you use say a 100% distilled water, its near zero resistance may create false triggering..... I experience that with washer fluid.
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