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Discussion Starter · #1 ·
Hi all. The cooling fan on my 97 9000 is not coming on. I''ve researched here and other sites and have replaced the thermostat and coolant temp sensor at the back of the head, but still the temp gauge in the car reads just above low, and the fan does not turn on. I've jumped the low and high speed relays, both speeds working fine on fan. What next? Resistor on the fan housing?
 

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First, you need to determine the temperature of your coolant when the engine has warmed up. If it is actually running below the set points for fan activation, it is not a main radiator fan control circuit problem.

The dash gauge is not the most reliable indicator and should not be the final word, but on the other hand it might very well be giving you an accurate reading of coolant temp. Just consider it as one possible indication.

I occasionally get chastised for suggesting this next "old school" diagnostic tool but I stand by it:

After the engine has had plenty of time to reach it's peak coolant temp, grasp the upper radiator hose and hold on to it. It should be hot enough as to be uncomfortable, but not so hot that you get burned - or are unable to hold it in your hand for at least a minute.

If it is not hot or even warm, your coolant is not coming up to normal operating temperature. Remove your new t-stat.Take it back to the parts store and tell them it was "bad out of the box".

If the coolant is truly running low, there is one other thing to check:

Turn the ACC system to OFF and check that the auxiliary (A/C condenser fan) is not running. It is mounted in front of the condenser and is visible by looking through the slats of the grille.

With the air conditioning turned to OFF, the compressor relay (which also supplies the auxiliary fan) should drop out and the aux fan should not run.
 

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Discussion Starter · #3 ·
Thanks for that. The hose gets quite hot. I'd say very hot. squeezing hose sends coolant through radiator to overflow. Seems to be no blockage. I'm beginning to suspect the sensor I replaced (between cylinders 2 and 3) is just for the ECU—for cold start. I just read something describing the sensor on the thermostat housing as being the one that controls the fan and gauge. I've read a lot of conflicting posts about this… does replacing this thermostat housing sensor sound like the best next step?
 

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The sensor located on the LH end of the cylinder head (adjacent to the thermostat) drives the dashboard temp gauge via the EDU (that's EDU not ECM). The Electronic Display Unit also controls the two (high and low speed) fan relays by grounding the negative legs of their associated coils.

That would be the one you want to look at closely.

The sensor that is a real PITA to get to (the one under the intake plenum) is dedicated to the ECM. The ECM uses the signal from that sensor to control various engine operations.

Saab says:

The temperature sensor is located in the intake manifold between the intake manifolds of cylinders 2 and 3 and is in contact with the engine coolant. The sensor is of the NTC type.

The engine control module measures the coolant temperature by applying 5 V to the sensor from pin 68 via an integral 2.74 kohm resistor. The sensor is grounded via pin 67 of the control module.

The ECM receives reference ground from the sensor ground lead to pin 66 to obtain a precise temperature measurement. The voltage across the resistor in the ECM is proportional to the coolant temperature.

The voltage is used to determine fuel injection duration for pre-injection as well as for cold starting and producing a richer fuel/air mixture during the warming-up period. Activation of closed loop and idling speed is also dependent on engine coolant temperature.
In the event of sensor failure or a break in the circuit, the engine control module will set a default temperature that is equivalent to the intake air temperature on starting and then increased by 1°C (1.8°F) every 150th engine revolution.
 

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There is also an issue with that fan controller ECU (Chengy calls it the EDU) which is inconveniently screwed to the back of the instrument panel. By all means change out both temperature sensors but don't be surprised if the problem remains.

Cooling system fan control is governed by this ECU. Failure modes can be interesting. If you verify that the engine is getting hot and the radiator is up to temperature (around 100C I should think) and the fan still isn't starting then suspect this ECU failure.

One symptom is an incorrectly reading temperature gauge since the ECU also damps the needle on the gauge to reduce complaints of overheating. I e the temperature gauge isn't, it's just an idiot light using a needle instead if a bulb. The gauge does not display engine temperature in reality. On mine the needle used to jump around just before the ECU failed completely. My symptom of final failure was the cooling fan stuck on until the battery went flat, several times before we finally figured this out.

Bad news is new ones are NLA. Because of the circuitry to this ECU jury rigging a switched system is pretty difficult.
 

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Discussion Starter · #6 ·
Thanks to both of you for your help on this. Really helpful. I've ordered the additional sensor and will update this thread after I've installed it. I also noticed a botch job in the wiring (one of the many hack jobs I've discovered done to my car when my wife was driving it and bringing it to a mechanic she liked) which could also be causing problems. Looks like the wires feeding the female end of the thermostat housing sensor connector had been cut at one time, instead of simply disconnecting the connector (which would have taken an extra two minutes) and then re-connected with bullet connectors and heat shrink. (which must have taken an extra ten minutes). Could be corrosion under that heat shrink...
 

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The 97's Dash gauge reads low.. By Design. Typically it points at 7 o clock rising to 8 'sometimes' Then when heat becomes an issue it pops right up to 10 /11 'o clock. Gaining instant attention by its elevated reading.
Also my Fan comes on very rarely.. it takes a quite hot day and or stop n go traffic to activate it.
Not saying there isn't a problem with yours.
But the Last 9000's had engine heating under far better control than Any of my previous/older 9000's ever managed.
Those would light up their twin! fans easily and (too?) often.
 

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Engine Cooling / Main Radiator Fan Operation 1995 - 1998

As info for future reference:


Cooling System » Description and Operation

Description and Operation:

Regardless of the position of the ignition switch, current is supplied to relay 155 via fuse 4 and to relay 81 via max fuse 2.

The radiator fan is controlled by the EDU control module.

The engine coolant temperature is measured by the EDU control module, which controls relay 155.

Single-Speed Radiator Fan
When the temperature reaches about 100 °C (212 °F) , relay 155 operates and radiator fan 37 starts. When the temperature drops to about 96 °C (205 °F) , the fan stops.

2-Speed Radiator Fan 366
In some markets, cars equipped with A/C have a 2-speed radiator fan for more efficient cooling.

The first stage (speed 1) operates as described above. The radiator fan starts at low speed

When the coolant temperature reaches 111 °C (232 °F) , relay 81 is grounded via the EDU control module. The radiator fan runs at full speed. When the coolant temperature drops to 107 °C (225 °F) , fan speed returns to speed 1 (low speed).

Cars With A/C
When the ignition is switched on, relay 433 operates and connects the A/C system's 3-stage pressure switch 166 in parallel with the EDU control module.

When the intermediate pressure switch closes, relay 155 is grounded via relay 433. Relay 155 operates and the radiator fan starts irrespective of the coolant temperature. When the pressure in the A/C system drops and the intermediate pressure switch opens, the fan will stop unless the coolant temperature is such as to cause the EDU control model to ground relay 155.

Radiator Fan Switch-off Relay 433
To prevent the battery from being drained when the radiator fan continues to run after the engine has been switched off, relay 433 breaks the circuit to the 3-stage pressure switch as soon as the ignition is switched off.

However, the EDU control module can cause relay 155 to operate so that the fan will continue to run at speed 1 (low speed). The time is then limited to 3.5 minutes .

Extra Pressure Switch 419
In certain markets, the A/C system is equipped with an extra pressure switch which controls relay 81. If the refrigerant pressure exceeds 22 bar, the contact will close. This causes relay 81 to operate and engages speed 2 on radiator fan 37.



COMPONENT ID

1. Battery in the engine bay.

37. Radiator fan motor on left-hand side of radiator.

75. Distribution block, battery, on the battery tray.

81. 2-speed radiator fan relay, in main fuse box in front of battery.

155. Radiator fan relay, in main fuse box in front of battery.

159. Distribution terminal (+15 circuit), in main fuse box behind the glove box.

166. Pressure switch for the radiator fan, on the receiver in front of the right-hand wheel housing.

210. EDU, in the main instrument display panel.

231. Distribution terminal (+54 circuit), in main fuse box behind the glove box.

342a. Fuse board in main fuse box in front of battery.

367. Resistor beside the radiator fan motor.

419. A/C cooling pressure switch (ME), under the radiator on the right-hand side.

433. Relay for disengagement of radiator fan, in main fuse box in front of battery.

2-Pin Connectors

H2-4 Adjacent to the radiator fan motor.

H2-85 Adjacent to the radiator fan motor.

3-Pin Connector

H3-23 Under the front bumper behind the right-hand fog light.

4-Pin Connector

H4-12 By the right-hand wheel housing beside the receiver.

10-Pin Connectors

H10-15 Behind the left-hand headlamp.

H10-25 Behind the left-hand headlamp.

Grounding Points

G30 Grounding point, left-hand structural member, behind the left-hand headlamp.

G31 Grounding point, right-hand structural member, behind the right-hand headlamp.


Schematics

Single Speed Fan:


Two Speed Fan:

 

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Discussion Starter · #9 ·
That's great info, thanks! I disconnected the switch to the EDU at the coupling in anticipation of the new switch arriving, and turned the ignition on to roll the windows down.The fan started running on low speed immediately. I switched the ignition off and timed it, and the fan ran for EXACTLY 3.5 minutes.
 

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It was that time delay function that failed in my EDU. The relay received no signal to switch off, randomly. Sometimes it worked normally, then didn't and the battery went flat from the fan running. Of course, the fact that power is always there could mean the fan was triggered by another fault in the EDU and it just mimicked failure of the timer.

Sounds like your issue may be confined to the sensor but, don't be surprised if it turns out to be the EDU.
 
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