Auxiliary Fan Control

[reson46]

I'm having issues with the auxiliary fan on the '91. At least some of the wiring/controls work because it comes on with the defrost and AC. That leads me to believe that any fuses and relays that control it are good. It does not come on when the engine temperature rises. I seem to remember that it is supposed to come on somewhere around 220 degrees - that doesn't happen.

 

I know on the HOs there are at least two sensors - on the back of the head by the firewall and in the thermostat housing. If the HOs are the same as the Renix, than the sensor on the head is for the temperature gauge? That would leave the sensor in the thermostat housing for the computer to control the fan, air/fuel mix, etc.?

 

I have replaced the sensor in the thermostat housing - same issues. Is this the sensor and associated wiring that I should be focusing on? If so, is there a way to test the sensor to verify that it is working correctly? Is there a way to test the wiring from the sensor? Is there a way to test the computer is working properly once it has received the input from the sensor?

 

Thanks,

Willy

[cracker]

I too would like to confirm that the sensor on the head next to the fire wall is, in fact, the guage temp sender only or for anything else..

[ParadiseMJ]

The head sensor is ONLY for the gauge/light.

 

On an HO the sensor for the computer/fan/etc. is on the t-stat

[cracker]

The head sensor is ONLY for the gauge/light.

 

On an HO the sensor for the computer/fan/etc. is on the t-stat

 

Thank you for clarifying that.

 

I had thought so but I wanted confirmation. :cheers:

[HOrnbrod]

The rear head sensor is for the temp gauge only. The one on the stat housing is for the aux fan. I test my aux fan by pulling the 2-wire plug off the stat sensor and shorting the pins in the connector. This applies a ground to pin 2 of the ECU to turn the fan on. If the fan doesn't come on, the sensor is bad or the wiring is faulty. If the wiring is open it should show up as a fault code (#22) using the key ON/OFF procedure.

[reson46]

The rear head sensor is for the temp gauge only. The one on the stat housing is for the aux fan. I test my aux fan by pulling the 2-wire plug off the stat sensor and shorting the pins in the connector. This applies a ground to pin 2 of the ECU to turn the fan on. If the fan doesn't come on, the sensor is bad or the wiring is faulty. If the wiring is open it should show up as a fault code (#22) using the key ON/OFF procedure.

 

Thanks! This is exactly what I was looking for. :bowdown:

 

I didn't realize you could check the fault codes of the '91s with the key ON/OFF procedure. If I remember correctly from past vehicles the procedure is key ON, key OFF, key ON, count the CHECK ENGINE flashes, pause, count the CHECK ENGINE flashes?

 

Thanks,

Willy

[HOrnbrod]

I couldn't format this, but you get the idea. :D

 

Reading Computer Codes

 

On 1991 to1997 models (1984 to 1986 V6 models as well as 1998 to 2002 follow) you have a way of reading for fault codes which can be accessed without any scanners like other models by reading how the check engine light flashes. Start by turning the ignition key to the last stop before it starts, on and off three times within 5 seconds ending in the on position on the third time, ( i.e. on, off, on, off then on and hold ). The check engine light will start to flash quickly with a small pause in between then a medium pause to indicate the next number in the to digit number and then a long pause before the next set of flashing for the next code. If all is well you will get a code 55 which would read like this: 5 fast flashes, medium pause then a further 5 flashes. This is how all codes end with is this 55 code if you have air conditioning or with a code 33 without and any other codes would have been before it separated by a long pause. The codes will remain after this test so you can cycle through it as many times as it takes to read them. After a problem has gone the code will be removed after 50 on off key cycles or if the battery left disconnected over night which will cause a code 12 though.

 

 

Code

Description

Most likely reason

 

11

No crank signal to computer.

Fault in wiring between crankshaft position sensor (CPS) and ECM ( PCM or computer ) or faulty CPS.

 

12

Battery disconnected.

Battery or power to the ECM disconnected in the last 50 key cycles.

 

13

MAP Sensor.

No change in Manifold Absolute Pressure (MAP) between engine off and on. Check circuit and MAP sensor.

 

14

MAP Sensor.

MAP sensor voltage too high or low. Check circuit and sensor.

 

15

Speed sensor or circuit.

No signal detected from speed sensor. Check circuit and sensor.

 

17

Engine running too cold.

Wrong or faulty thermostat. Check also sensor and circuit for fault.

 

21

Oxygen sensor or circuit.

O2 sensor or wiring faulty.

 

22

Coolant sensor or circuit.

Check temp sensor and wiring.

 

23

Intake air temp or circuit.

Check air temp sensor and wiring.

 

24

Throttle Position Sensor (TPS)

Check TPS sensor and wiring.

 

25

Idle Air Control circuit (IAC)

Check IAC sensor and wiring.

 

26

Injector circuit resistance.

Peak injector current has not been reached or injector circuits have resistance

 

27

Fuel injector control circuit.

Will need specialist diagnostics.

 

31

Evaporative control circuit.

Fault in fuel evaporative control circuit or hoses.

 

33

Air conditioning clutch relay.

Wiring to A/C clutch fault.

 

34

Cruise control circuit.

Fault in circuit.

 

35

Cooling fan relay.

Check relay and circuit.

 

36

Air switch solenoid circuit.

Air switch solenoid circuit (non-turbo) or the waste gate solenoid on turbocharged models

 

37

Torque converter clutch.

Needs specialist or dealer diagnostics.

 

41

Alternator field switch.

Switch not operating correctly and check charging system.

 

42

Automatic shutdown relay.

Check relay and circuit. Needs specialist or dealer diagnostics.

 

43

Misfire.

Misfire in one or more cylinders.

 

44

Battery temperature sensor.

Needs specialist or dealer diagnostics.

 

46

Battery over voltage.

Check charging system.

 

47

Battery under voltage.

Check charging system.

 

51

O2 detects lean mixture.

Check sensor and circuit and for vacuum leaks.

 

52

O2 detects rich mixture.

Check fuel injection system and sensor.

 

53

Powertrain Control Module.

PCM (ECM) fault. Needs specialist or dealer diagnostics.

 

54

Distributor sync pickup.

Change sync sensor in distributor.

 

55

End of code.

Trouble codes finished or none recorded.

 

61

BARO solenoid

BARO solenoid failure

 

62

Emissions reminder.

Emissions maintenance reminder. Needs specialist or dealer diagnostics.

 

63

Controller failure.

EEPROM write denied. Needs specialist or dealer diagnostics.

 

64

Flexible fuel sensor.

Flexible fuel (methanol) sensor indicates concentration sensor input more/less than acceptable voltage

 

65

Manifold tune value.

Manifold tune valve solenoid circuit open or shorted

 

66

TCM to PCM failure.

No message from the Transmission Control Module (TCM) to the Powertrain Control Module (PCM)

 

72

Catalytic converter circuit.

Needs specialist or dealer diagnostics.

 

76

Fuel pump bypass relay circuit.

Needs specialist or dealer diagnostics.

 

77

Cruise control system.

Check power to cruise control solenoids.

[J B Cuz]

I pulled up the wiring diagram for a 1991 and the aux fan is controlled by the ECU pin #31 DK BLU/PK it goes in the the power distribution center cooling fan relay and controls the ground to turn the fan on and off. After looking at the wiring I think it would be th sensor on the t stat housing that the ECU is using to determine the temp for turning the fan on and off.

 

J B Cuz

[reson46]

I couldn't format this, but you get the idea. :D

 

Thanks again! :D

 

Willy

[HOrnbrod]

I pulled up the wiring diagram for a 1991 and the aux fan is controlled by the ECU pin #31 DK BLU/PK it goes in the the power distribution center cooling fan relay and controls the ground to turn the fan on and off. After looking at the wiring I think it would be th sensor on the t stat housing that the ECU is using to determine the temp for turning the fan on and off. J B Cuz

 

Correct. I use a dash switch to apply a ground to ECU pin 31 as a fail-safe in case either of my electric fans go belly-up. :D

[reson46]

I pulled up the wiring diagram for a 1991 and the aux fan is controlled by the ECU pin #31 DK BLU/PK it goes in the the power distribution center cooling fan relay and controls the ground to turn the fan on and off. After looking at the wiring I think it would be th sensor on the t stat housing that the ECU is using to determine the temp for turning the fan on and off. J B Cuz

 

Correct. I use a dash switch to apply a ground to ECU pin 31 as a fail-safe in case either of my electric fans go belly-up. :D

 

I thought you had a SPAL? :hmm:

 

I've got code 22. :( Jumping the wires in the temperature sensor connector didn't turn the fan on. I'm guessing the wiring is bad somewhere along the way. Does anybody know where I can find a wiring diagram for a '91? I'm not looking forward to ripping apart the harness. It all looks so neat and tidy compared to the spaghetti in the '88. :cry:

 

Thanks,

Willy

[HOrnbrod]

I thought you had a SPAL? :hmm:

 

I've got code 22. :( Jumping the wires in the temperature sensor connector didn't turn the fan on. I'm guessing the wiring is bad somewhere along the way. Does anybody know where I can find a wiring diagram for a '91? I'm not looking forward to ripping apart the harness. It all looks so neat and tidy compared to the spaghetti in the '88. :cry: Thanks, Willy

 

I do have a Spal controller for the electric fan that replaced the clutch fan. The stock aux fan works off the stock sensors. The dash switch is only backup in case my Spal controller dies so I can still turn on the aux fan if I need to. :D

 

I have the 91 electrical FSM but no way to scan what you need. Try checking the stat temp sensor connector pins for continuity first. One goes to ground; the other goes to pin 2 of the ECU. Might just be a bad ground, hopefully.