[CFM]

Noticed a few threads on this so I thought I'd add my experience to the list. One of the other threads involved a cut wire to the ECT sensor. In my case, the cause was IAT sensor related. So both circuits should be checked if you experience this issue.

I was recently doing some testing utilizing a jumper harness between the Multifunction Sensor(MAF, IAT, Baro, Humidity) and its factory connector. Fired up the engine and noticed the fan on high. Shut down and the fan kept running. I found that a pin for the IAT sensor had backed out of one of the connectors in the jumper harness. Fixed that and fan operation was back to normal.

Here are some excerpts from the service manual.....

Description and Operation:
LT1/LF4 Engine

Cooling fan speed is effected by many different conditions and can be adjusted from 20% to 99% duty cycle (PWM), 90% is considered high speed fan. When multiple cooling fan speed requests are received the ECM uses the highest cooling fan speed of all the requests. The ECM commands the cooling fan ON under the following conditions:

- Cooling fan duty cycle starts when engine coolant temperature reaches approximately 101°C (214°F) and reaches high speed at temperatures above 109°C (228°F).

- Cooling fan duty cycle starts when A/C pressure reaches approximately 975 kPa (141 psi) and reaches high speed at A/C pressures above 2100 kPa (305 psi).

- At transmission oil temperatures above approximately 112°C (234°F) the cooling fan duty cycle will be commanded to high speed.

- After the vehicle is shut OFF if the engine coolant temperature at key-off is greater than 113°C (235°F) or the A/C pressure is greater than 2300 kPa (334 psi) the cooling fan duty cycle is set to 55%, low speed. If the coolant temperature drops below 107°C (225°F) and the A/C pressure drops below 1800 kPa (261 psi) the fan will shut OFF. The fan will automatically shut OFF after 300 seconds. regardless of coolant temperature.

Diagnostic Aids

- Certain resistance conditions with IAT or ECT sensors may cause unwarranted cooling fan activation. If the ECM is commanding the cooling fan ON for no apparent reason and without any component or system DTCs set, the IAT or ECT sensor may be skewed. If this condition is suspected, refer to the temperature versus resistance tables in the appropriate engine controls subsection.

- A delay or ramp up of approximately 12 seconds may occur before the cooling fan activates or changes speed when being commanded with a scan tool.

- In order to set certain DTCs the PCM must command the Cooling Fan system On. Using the scan tool to operate the Cooling Fan will not set certain DTCs. In these cases run the vehicle until it reaches an appropriate condition for the PCM to command the Cooling Fans On.

[BradfordCamaro]

Thank you
Mine does this. But mine may be tune related.
I will go over my wiring.

Great info.

[Eldi Z]

Originally Posted by CFM

Noticed a few threads on this so I thought I'd add my experience to the list. One of the other threads involved a cut wire to the ECT sensor. In my case, the cause was IAT sensor related. So both circuits should be checked if you experience this issue.

I was recently doing some testing utilizing a jumper harness between the Multifunction Sensor(MAF, IAT, Baro, Humidity) and its factory connector. Fired up the engine and noticed the fan on high. Shut down and the fan kept running. I found that a pin for the IAT sensor had backed out of one of the connectors in the jumper harness. Fixed that and fan operation was back to normal.

Here are some excerpts from the service manual.....

Description and Operation:
LT1/LF4 Engine

Cooling fan speed is effected by many different conditions and can be adjusted from 20% to 99% duty cycle (PWM), 90% is considered high speed fan. When multiple cooling fan speed requests are received the ECM uses the highest cooling fan speed of all the requests. The ECM commands the cooling fan ON under the following conditions:

- Cooling fan duty cycle starts when engine coolant temperature reaches approximately 101°C (214°F) and reaches high speed at temperatures above 109°C (228°F).

- Cooling fan duty cycle starts when A/C pressure reaches approximately 975 kPa (141 psi) and reaches high speed at A/C pressures above 2100 kPa (305 psi).

- At transmission oil temperatures above approximately 112°C (234°F) the cooling fan duty cycle will be commanded to high speed.

- After the vehicle is shut OFF if the engine coolant temperature at key-off is greater than 113°C (235°F) or the A/C pressure is greater than 2300 kPa (334 psi) the cooling fan duty cycle is set to 55%, low speed. If the coolant temperature drops below 107°C (225°F) and the A/C pressure drops below 1800 kPa (261 psi) the fan will shut OFF. The fan will automatically shut OFF after 300 seconds. regardless of coolant temperature.

Diagnostic Aids

- Certain resistance conditions with IAT or ECT sensors may cause unwarranted cooling fan activation. If the ECM is commanding the cooling fan ON for no apparent reason and without any component or system DTCs set, the IAT or ECT sensor may be skewed. If this condition is suspected, refer to the temperature versus resistance tables in the appropriate engine controls subsection.

- A delay or ramp up of approximately 12 seconds may occur before the cooling fan activates or changes speed when being commanded with a scan tool.

- In order to set certain DTCs the PCM must command the Cooling Fan system On. Using the scan tool to operate the Cooling Fan will not set certain DTCs. In these cases run the vehicle until it reaches an appropriate condition for the PCM to command the Cooling Fans On.

Thanks for this detailed write-up.
I encountered a similar issue (fan on full speed), however, in my case the Temp gauge remained pegged at low without any movement (despite engine being at normal Temp range) and AC compressor would not kick in.
I was told tjhat such phenomena is associated with "safe mode". This can be triggered by wiring, sensors or even inductance / electromagnetic disturbances related to the wiring going to the ECM from the OBD port.

Could you also see apart from the Fan behavior, the Temp gauge and AC operation?

[CFM]

Originally Posted by Eldi Z

Thanks for this detailed write-up.
I encountered a similar issue (fan on full speed), however, in my case the Temp gauge remained pegged at low without any movement (despite engine being at normal Temp range) and AC compressor would not kick in.
I was told tjhat such phenomena is associated with "safe mode". This can be triggered by wiring, sensors or even inductance / electromagnetic disturbances related to the wiring going to the ECM from the OBD port.

Could you also see apart from the Fan behavior, the Temp gauge and AC operation?

Yes. Open circuit/disconnected engine coolant sensor typically reads something like -40* at the ECM, and the ECM tells the instrument cluster what to display on the gauge. Should be a trouble code for ECT circuit high as the ECT sensor is 1/2 of a voltage divider circuit with the other side connected to +5V through a resistor and the sensor being a temperature sensitive variable resistor(thermistor) connected to ground. AC operation is likely disabled when the ECM does not know what the engine temp is.

[Eldi Z]

Originally Posted by CFM

Yes. Open circuit/disconnected engine coolant sensor typically reads something like -40* at the ECM, and the ECM tells the instrument cluster what to display on the gauge. Should be a trouble code for ECT circuit high as the ECT sensor is 1/2 of a voltage divider circuit with the other side connected to +5V through a resistor and the sensor being a temperature sensitive variable resistor(thermistor) connected to ground. AC operation is likely disabled when the ECM does not know what the engine temp is.

O.K. interesting.
Could you maybe take some pictures of all the connectors that I should look into ? This would help me identify and then check what is going on with them.

[CFM]

Originally Posted by Eldi Z

O.K. interesting.
Could you maybe take some pictures of all the connectors that I should look into ? This would help me identify and then check what is going on with them.

This view is with the air duct removed. Coolant sensor is #2. The connector is #1(shown unplugged). Black/white wire is signal ground. Blue wire is the signal. Check the sensor, connector and both wires.

[Eldi Z]

Originally Posted by CFM

This view is with the air duct removed. Coolant sensor is #2. The connector is #1(shown unplugged). Black/white wire is signal ground. Blue wire is the signal. Check the sensor, connector and both wires.

Thanks! This one I did check and everything looks nice and tight.
You mentioned the IAT sensor as well... where should I look? This was your issue, correct?

[CFM]

Originally Posted by Eldi Z

Thanks! This one I did check and everything looks nice and tight.
You mentioned the IAT sensor as well... where should I look? This was your issue, correct?

IAT is part of the MAF sensor which is in the intake air duct right next to the air filter box. It is the connector to the right of the ECT connector in the above pic. It would not affect your temp gauge.

[CFM]

Originally Posted by Eldi Z

Thanks! This one I did check and everything looks nice and tight.
You mentioned the IAT sensor as well... where should I look? This was your issue, correct?

You can check the circuits to the coolant sensor......

1. Key on/engine off..... hold the start button for up to 10 seconds without touching the brake...everything on the instrument cluster will light up and you should hear the fuel pump run briefly and the throttle click.

2. Unplug the coolant temp sensor and test with a digital multimeter. Should be 0 ohms between the terminal of the black wire and the engine block. Should be near 5V between the 2 terminals.

If those test OK, test or replace the coolant temp sensor.

[Eldi Z]

Originally Posted by CFM

You can check the circuits to the coolant sensor......

1. Key on/engine off..... hold the start button for up to 10 seconds without touching the brake...everything on the instrument cluster will light up and you should hear the fuel pump run briefly and the throttle click.

2. Unplug the coolant temp sensor and test with a digital multimeter. Should be 0 ohms between the terminal of the black wire and the engine block. Should be near 5V between the 2 terminals.

If those test OK, test or replace the coolant temp sensor.

Thanks a lot for this information!
I shall test the wiring / circuit it if the problem re-occurs.

Since the car is almost brand new, I have a feeling that the issue might relate to some magnetic influence on the OBD wiring.
In my job I use Induction circuits with strong magnets attached to them.

A couple of weeks ago, I accidentally placed one of these circuits inside the side bins of the driver's door and forgot all about it.
Once I removed this device I did not have this "Full blast Fan" phenomena re-occur.
I shall continue monitoring the situation and hope that removing the magnets solved the issue.
BtW: Before I took these circuits with me to work in the 1LE (only had them transported to work in my DD Seat Leon), it also never happened in the 1LE. Strange thing
Conclusion: When going to work don't drive the 1LE, it should only be driven for fun days

[CFM]

Originally Posted by Eldi Z

Thanks a lot for this information!
I shall test the wiring / circuit it if the problem re-occurs.

Since the car is almost brand new, I have a feeling that the issue might relate to some magnetic influence on the OBD wiring.
In my job I use Induction circuits with strong magnets attached to them.

A couple of weeks ago, I accidentally placed one of these circuits inside the side bins of the driver's door and forgot all about it.
Once I removed this device I did not have this "Full blast Fan" phenomena re-occur.
I shall continue monitoring the situation and hope that removing the magnets solved the issue.
BtW: Before I took these circuits with me to work in the 1LE (only had them transported to work in my DD Seat Leon), it also never happened in the 1LE. Strange thing
Conclusion: When going to work don't drive the 1LE, it should only be driven for fun days

Could just have been a weak connection somewhere or some water got into the connector if it only occurred once.

[Eldi Z]

Originally Posted by CFM

Could just have been a weak connection somewhere or some water got into the connector if it only occurred once.

Water into the connector is something I did not think of. Is the connector prone to having water get to it? Nobody ever mentioned this as an issue...
Could the water enter I.E. from the scoops on the hood maybe?

[CFM]

Originally Posted by Eldi Z

Water into the connector is something I did not think of. Is the connector prone to having water get to it? Nobody ever mentioned this as an issue...
Could the water enter I.E. from the scoops on the hood maybe?

The connectors are water resistant, not waterproof. One time I washed the engine bay of my AV back when it was mostly stock and got the hood insulation wet. On the way home I turned a corner and I guess some water dripped onto the throttle connector which triggered REP (reduced engine power/limp) mode. Just dried the connector with compressed air to clear that up.

The hood vent does drain in that area. Guessing that it could blow back onto the ECT connector under the right conditions. That connector uses the same type of terminals and seals as the throttle connector of my Av.

There should be trouble codes set and stored though when the ECM loses a sensor signal or the signal is out of range. The codes are only stored for a given number of key on/drive cycles though if they are intermittent. The number of cycles varies with the particular code.

[Eldi Z]

Originally Posted by CFM

The connectors are water resistant, not waterproof. One time I washed the engine bay of my AV back when it was mostly stock and got the hood insulation wet. On the way home I turned a corner and I guess some water dripped onto the throttle connector which triggered REP (reduced engine power/limp) mode. Just dried the connector with compressed air to clear that up.

The hood vent does drain in that area. Guessing that it could blow back onto the ECT connector under the right conditions. That connector uses the same type of terminals and seals as the throttle connector of my Av.

There should be trouble codes set and stored though when the ECM loses a sensor signal or the signal is out of range. The codes are only stored for a given number of key on/drive cycles though if they are intermittent. The number of cycles varies with the particular code.

O.K. I understand. Let me monitor again after leaving the car wash... If this is the issue, then I am partially going to be relieved because the culprit can be isolated. Concern then remains, how to keep the water from coming back. I almost never encountered anyone here on the forum complain about this happening and there are days in various regions with heavy rain every day.