Engine coolant fan not shutting off after having properly kicking on at 217 deg

Engine coolant fan not shutting off after having properly kicking on at 217 degrees and all this subsequent to 40 minute idle time temperature ascent from ambient temperature (95 degrees) without ever achieving a stable equilibrium point... previously always at 198 degrees there was a stable equilibrium point.

2008 Chev Cobalt 2.2 L. Manual transmission only 48,000 original miles no collision damage.no engine light present. Aside from occasional tac-speedometer flip out rail to ral and in between flutter gyrations ... no previous system failures on this cobalt.

Maintenance record: 3000 mile ... oil, air filter,,, Coolant system Flush annually... Break system flush every 4 years,

Where I am now:

I confirmed wire harness, relay, and Engine Coolant temp Sensor, fan and control circuit driver pull down ... (negative side switched relay control out of the computer does turn on fan... Aside from that, in addition, I installed new thermostat

From there, (computer) just does not then toggle the control line shutting down the fan... I testing item for item respectively via Paul's recommended tests..

Directions from here:

1) if Driver circuit Good, that tells me some other problem then ??? But What? In this case, this could only be, if and only if, ECM Programming and sensor input has the ECM thinking engine is in overheat mode even during dashboard engine coolant temp indicator indicating temperature decent to and past 150 degrees and still falling ??

2) if Driver Circuit damage ... this tells me “high speed fan relay driver circuit” can turn on fan but cannot then turn off said fan ??? Does that even make sense or seem likely

(3) something else is going on with this high speed fan circuit and the cooling system overheat management system.

Hi John I am going to move your question over into the Repair Questions section where it should get more attention

When cold can you command the fan on and off using a bi-directional command or even just view if it is commanded on ?

The fan can be triggered when the engine computer detects a number of inputs from for example the AC Trinary Switch or Pressure sensor.

the direction now. is the ECM seeing ECT and is the driver transistor and external connectivity functional?

For sure, i’ll next Be viewing cold condition status ... commanded on or not... it’s up next



As For these other potential directions, Thank you, Bringing new factors, ie. , (1) when cold status, 2) AC, and (3) pressure) to the mix

Along those lines, Thinking of and comparing ac versus ECT triggering inputs schematically... two things:

1) in this case, schematic detail has it down to ... differentiating ac versus ECT trigger as being implemented in two externally different circuit paths respectively.


I have confirmed and verified entire ac “as it turns out , low speed fan” function and i verified and confirmed “ECM-FAN” circuit portion “as it turns out, high operating speed” Fan functionality ...

Your input is highly regarded

What scan tool are you currently using? Like Andy said, I would definitely want to know what the PCM is seeing for coolant temp and when/if it is commanding the fan off and on.

In my DIYer opinion, the best budget bi-direcitonal tool is the Autel DS808. In the higher end, the Bosch ADS325 has my attention.

I currently do not have one but am in process of evaluating and choosing for purchase soon

By the way! You said best budget choice ...

but

If budget weren’t so Much at issue what alternative product lineup of multiple choices might you be willing to
consider in order of most expensive feature rich downwards just above what you have mentioned here??

Everyone needs a plug-and-play, handheld reader/scanner that doesn't have to be charged and can fit in a glove box. My advice is to start with one of those and learn to read scan data while you decide on a full featured tool. I started out with an old SnapOn Modis and an Autel MD802. I ended up selling the Modis to buy a handeld lab scope. I've looked several times, but have yet to upgrade from either one. If money were no consideration, I would at least have a Pico, an Autel, and a Bosch.

For your cooling fan issue, I think looking at scan data is an absolute necessity.

The scanner I get I. hope to ensure my vehicles are represented in those supported in bi directional functionality but how do you approach determining that?

I have a 2008 Chevy cobalt 2.2 liter standard Number1G1AK58F887243099

And 2003 Ford Lariat super cab
5.4 Liter?

You said best budget choice ... but

If budget weren’t so Much at issue what alternative product choices might you consider ?