Fans not kicking in

[whytie]

Got a car here and the fans are not kicking in, all fuses are fine, relay is fine. I bridged the relay and the fans come on no probs. so I guessed it would be the thermo transmitter so I tested pin 18 on the ecu and it started at 3.5v and dropped to around 1.5v before I turned engine off. I also tested an other ecu.

I would of thought the voltage would rise not dropped to trigger the fans?

 

[whytie]

I also checked PIN number 9 which is radiator relay which should be 12v with engine running and 9v when fans kick in. I think pin 9 earths to complete the circuit to trigger the relay then the fans.

im just a bit confused at what to look for next ?

 

[Fast Guy]

Is your air con removed?

 

[whytie]

No not removed and the fans don't come on when I turn on the air con

 

[Fast Guy]

Pull the relay and check you have 2 power feeds. One should be permanent and the other should work with the ignition switch. If no switched feed then check the fuse box for a blown 10A fuse. If there's no permanent feed then check the fusible links in the engine bay. Try another relay if they're both OK.

 

[red reading]

Ecu triggers are pull to ground, so the ecu figures are right..do as carl has said.

 

[whytie]

Done what Carl has said I've got a constant live and got a live feed when I switch the ignition on, also swapped the relay from an other known good one.

Everything seems to be working as it should and I'm getting all the right signals.

 

[Fast Guy]

Check for continuity between the ecu and the relay and that's OK it's looking like the ecu not sending the signal to me. Could be engine temp sensor not reading high enough to tell the ecu to turn the fans on.

 

[whytie]

Checked the continuity also compared to an other car which was the same. Swapped ecu also. Im going to swap the gauges in case it's going of the scale but temp isn't high enough to trigger fans

 

[whytie]

Should the ecu see 0v from the temp transmitter to trigger fans?

 

[geoff pine]

When my fans would not come on it was the thermostat that was stuck open .

 

[whytie]

Thermostat is fine.

I managed to pull the plug of the transmitter while the car was running and the fans kicked in straight away. So I know the whole circuit is now good and the ecu is sending the correct signal.

I guessed I must have a fault transmitter so I swapped it with a spare but the fans still didn't kick in which is pretty disappointing. The transmitter I fitted was from a cooling pipe that had been sitting for years so ill try another.

does anyone know what voltage the ecu needs to see to trigger the fans the lowest I seen it before I switched of engine was 1.17v

 

[Fast Guy]

I don't know the voltage, but there's two sensors, so don't rely on the gauge to know if your hot enough. Only the ecu knows what the other sensor is reading unless you can hook into the ecu.

 

[whytie]

With my hand on the engine I know that's very hot, I will change the gauge temp sensor just in case I'm turning car off prematurely.

i really need to find someone with a consult to read the actual temp.

 

[Fast Guy]

Engine temp sensor works on resistance. http://www.gtirworkshopmanual.com/default.aspx?v=1092

The engine will get hot wether as long as it's turned on, so doesn't really tell you anything.

what do you mean turning it off prematurely?

 

[vss irvine]

Or you could just buy a laser thermometer.

Or borrow mine if you go down and see my old man.

 

[warpspeed]

With my hand on the engine I know that's very hot, I will change the gauge temp sensor just in case I'm turning car off prematurely.

i really need to find someone with a consult to read the actual temp.

I have a consult at the garage....you can borrow it if you want

 

[whytie]

Little update on my fans not kicking in issue, I had to leave this for a week and work on something else as it was doing my tits in.

i tested everything and everything seemed to be fine all correct readings. I tested a working car to compare results and when the temp transmitter voltage drops to 0.8 volts that's when the fans kick in. When testing the other car it gets to around 1.2 volts when the water temp gauge starts to read hot. I decided to keep it running and sure enough when it dropped to 0.8 fans kicked in.

I'm glad the fan circuit is all working and the ecu side of it is all ok. Know I've changed the temp gauge sensor, temp transmitter and also the car gauges and its still reading hot on the gauges. Ill have to get a thermometer to check actual temps as something just isnt right.

For anyone that doesnt have a nissan consult, its handy to know that testing pin 18 on the ecu you need to see 0.8 volts for the fans to kick in.

 

[The Doc]

Have you checked and cleaned the earths on the engine and battery/chassis? As any fault there will cause the sensors to miss read /or normally under read and give the symptoms you have.