2003 Chevrolet Malibu

Engine Cooling problem
2003 Chevy Malibu 6 cyl Front Wheel Drive Automatic 130000 miles

I'm the owner of this vehicle and am relaying the problem as my mechanic has described it to me:

The hi-speed radiator fan is not coming on when the temperature goes over 96 degrees centigrade. (The low-speed fan is operating normally.)

The engine coolant overflows as a result.

We have installed a new engine temperature sensor, a new thermostat and even reprogrammed the Engine Control Module.

What we don't understand is that when we unthread the engine temperature sensor from the housing, leaving the electric connector hooked into it and with the ignition key on, when we place the sensor in a bowl with water and heat it to 96 degrees centigrade the system responds and the fans come on like they should when the sensor is threaded into the thermostat housing.

A thermoswitch has been installed temporarily so that the vehicle can be driven.
December 2, 2009.

That would make me look at a different reason and the fan is not the problem
if system is malfunction PCM would pick it up and give you a check engine light and service message

is the engine overheating?
Or you are losing coolant
if its a coolant loss that you are after check intake manifold as they very common and the cause of almost every GM V6 we worked on in the past few years

Dec 2, 2009.
If the high-speed fan is not coming on, how is the fan not the problem? According to the mechanic, no service message/code was recorded. Is the engine overheating? Yes. Is coolant being lost? Yes, but only after the temperature exceeds 96 degrees centigrade. Below that temperature, the low-speed fan functions and there is no coolant loss. The mechanic says there is no intake manifold leak; coolant is circulating in the system.

Dec 3, 2009.
So to recap,

1) Engine overheats
2) Coolant overflows
3) The high-speed fan has been determined to not activate.
4) When high-speed fan is manually activated, engine does not overheat and coolant does not overflow.
5) a) The ECM (Electronic Control Module) controls fan activation, is this not correct?
B) ECM has been re-programmed.
6) New thermostat has been installed.
7) New engine temperature sensor has been installed.
8) Intake manifold is functioning normally.
9) This we feel is the main issue. It seems to be clearly the main issue. Please advise if we are misguided on this: " The engine temperature sensor screws into the housing. On the other end of the sensor are two wires that connect to the ECM. When sensor is screwed into housing and its wires are connected to ECM, high speed fan doesn't come on and coolant overflows. When sensor is unscrewed from housing and heated to 96 degrees centigrade in a pail of water, high speed fan comes on and coolant doesn't overflow! The two wires that connect the sensor to the ECM have been checked and are transmitting proper voltage.&Quot; ?

Dec 4, 2009.
Battery positive voltage is supplied to the Cool Fan #1 relay from the COOL FAN #1 fuse.

The powertrain control module (PCM) controls the Cool Fan #1 relay by grounding the low speed cooling fan relay control circuit via an internal solid state device called a driver.
Battery positive voltage is supplied to the Cool Fan #2 relay from the COOL FAN #2 fuse. The powertrain control module (PCM) controls the relays by grounding the high speed cooling fan relay control circuit.
When the PCM is commanding a relay on, the voltage potential of the control circuit should be low, near 0 volts. When the PCM is commanding the control circuit to a relay, the voltage potential of the circuit should be high, near battery voltage. If the fault detection circuit senses a voltage other than what is expected, the DTC will set.

The PCM will monitor the control circuit for the following:
A short to ground
A short to voltage
An open circuit
An open relay coil
An internally shorted or excessively low resistance relay coil.
When the PCM detects any of the above conditions, DTC will set and the affected driver will be disabled.

Dec 4, 2009.
I have already written that the Electronic Control Module has been reprogrammed. The facts that you outlined in your prior comment are on our checklist. The problem is not resolved.

Dec 9, 2009.
We've analyzed one other thing and don't feel it's related to the current problem.

In the past year, the camshaft and valve lifters were replaced. To get at the camshaft, the engine had to be removed from the vehicle. The coolant problem first occurred after this repair. BUT, the coolant overflow problem was resolved quickly. It wasn't until a few months later that the problem recurred which is the point we're now at.

We're getting coolant circulation behind the engine temperature sensor. If the gaskets weren't properly placed during the camshaft replacement, the coolant circulation would be impaired, correct? [See all earlier comments.] Thanks.

Dec 10, 2009.
Is there anything else that can be done to troubleshoot this problem?

Dec 19, 2009.
My opinion on the subject was that you mechanic is looking at the wrong reasons
and I do understand that the fan need to run at high but that when coolant temp reach a certain temp
and the PCM order high fan by grounding the high fan relay
if its an electrical system you would have a code as the PCM always running a self, sensors and circuit tests
we know its not the PCM as it was checked and reprogrammed
that leave mechanical and engine
my suggestion is to have it check by another tech and get another opinion I think something is missing

Dec 19, 2009.
Do you have an opinion as to what sort of mechanical or engine issues could produce such a result? The vehicle is being run without the catalytic converter. I do notice when the vehicle is being run and after the engine is shut off that there are clicking noises. It is as if the coolant wasn't cooling the metal! But I was told the noise is associated with gases expanding/contracting due to the lack of an installed catalytic converter. [I'm in Latin America right now. If I was in the United States, I'd take it to a Chevrolet dealership to resolve the problem. I have contacted a dealership in Arizona and have asked them to take a look at this post at 2carpros for additional input. They may or may not be able to offer any advice.]

Dec 19, 2009.