Cooling fans run anytime the car is running

I have a 2003 Neon with 74,000 miles. I’m getting code p0481 and both cooling fans run nonstop within 5 or so seconds of starting the car. The relay has been changed, the AC and def aren’t on. I’ve pulled the connecter off of the coolant temp sensor, the high and low AC pressure sensors and the fans continue to run. Ideas?

Inspect the PCM and wiring for damage. The PCM is located in front of the transmission and vulnerable to damage from the core support striking sidewalks and parking stops.

Check the radiator fan control circuit for a short to ground, if OK the PCM has failed. BTW, do the fans stop with the relay removed?

Might the fans be running for a reason that you’d want them to be running? I might be looking for a malfunction in the fan hardware if I were in your shoes too, but don’t rule out that they might be keeping the engine from overheating if there is a problem elsewhere in the cooling system, such as a partially-clogged radiator, a partially clogged thermostat, or some other issue that would make the fans come on and stay on because the engine is unable to lower the temperature to the point where the fans would normally shut off.

Thanks everyone. I’ll double check the fan control circuit for shorts. They do stop when either the relay or fuse is pulled. I’m leaning toward the PCM. Physically it doesn’t seem to have been damaged but the two bolts holding the bottom of the bracket are missing. The fans run from from a cold start in 25 degree weather. The radiator builds pressure normally.

So far no luck, changed the ECM/PCM and still get p0481 and fans running. Other ideas?

You have to check the control circuit. Remove the relay, disconnect the PCM connectors and check the control circuit for short to ground with an ohm meter.

Good idea above to check input pin(s) to the fan relay with the relay removed. Before checking the ohms to ground, be sure everything is turned off. Next check the voltage on those relay input pins when the engine is turned on and the fans would be running (if you hadn’t removed the relay).

Only had a few minutes today, but so far I haven’t found a short to ground. The pins with the relay removed and the car off show a little over 12v and then each pair shows around 13v with the car running and AC/def off.

A fan relay will usually have one pair of pins for the relay control (the relay coil), and a second pair for the switched power (one pin for the battery power input, and one pin for the switched battery power output). Are you saying all four of those pins are 13 volt when the engine is running?

13 on each pair. I have a second temp sensor to put in as of today too. Something tells me the one I’d changed out might be bad. I’ll hopefully update tomorrow. Thanks!

By “13 volts on each pair”, do you mean you measure the voltage one pin to the other on a pair? And both pairs measure 13 volts potential difference? If so, that suggests the control input to the relay (the coil) is programmed to be energized and in the “on” state for some reason. So the problem then wouldn’t be a faulty relay. The relay is just doing what it is supposed to do, turning on. Whatever is causing the control signal to turn the relay on – when it shouldn’t presumably – is what you are looking for. Doesn’t sound like a ground problem at the relay either.

There is something a little odd about the 13 volts though. Usually the battery voltage would be 13.5-15.5 volts with the engine running. But if the battery was fully charged, could be 13 I suppose.

With the ignition off there should be no power on the control circuit for the fan relay, pins 85 or 86. Check the relay for pin number identification.

If you can, insert the relay half way in and probe the side of the relay pins to measure voltage inputs. The PCM controls the fan relay by providing a ground, the control circuit should not be grounded when the temperature gauge reads cold and the A/C and defroster are off.

If you can make out my chicken scratch, with the ignition off there is 12.2 between 87 and 30 and the battery terminal on the PDC and 30. When the ignition is on, but the motor hasn’t been started, there’s 12.2 between all the pins and 30 as the ground and 12.2 between 87 and 85.

Also I do get 13.5 with the motor running. And thanks to everyone for the continued help.

For the 03 Neon L4 2L vin C engine here’s what I’m seeing. Unfortunately the pin numbers don’t match up with OP’s drawing. I’m presuming that’s the number printed on the relay, not where the relay plugs in. The diagram I’m looking at is probably for the pin numbers where the relay plugs in. OP may be able to cross reference them using the wire colors below

A relay contains coil circuit and a switched power circuity. The coil circuit is powered up in run & start, through fuse 10 or 11. So Pin 69 should have battery power (between the pin and chassis ground) whenever the key is on or start, powered via a DB/WT wire (dark brown blue w/white stripe presumably). When it wants the relay turned on, the PCM grounds pin 70 via a DB/PK wire which completes the coil circuit.

The switched power circuit is powered from fuse 6, then via a GY wire to pin 73. Pin 73 should have battery power (pin to chassis) at all times. When the coil circuit is completed, the switch is thrown giving battery power to pin 71, then to the fan motor via a Y wire.

The way I’d test it is using a test light. If it lights between pin 69 and 70 (with the relay removed), that means the PCM is programming the radiator fan to turn on, or there’s a short in the DB/PK wire to chassis ground.

Thanks, right, the numbers are printed on the relay.

The wires in my pic of the white clip below the relay in the same position as my drawing. 30 is yellow, 86 blue/white, 87 gray, blue/pink 85. If oriented the same as yours, where do my pins correspond? I believe 87 on mine corresponds to 73 on yours. My drawing is standing at the drivers fender with 86 closest the fender and 85 closest the motor with 30 toward the front of the car.

This is my guess how the pin numbers match up

Pin ----- Wire Color --------- Relay pin number

69 — Dark Blue/White ---- 86 ------- Battery Power to relay circuit in on/start (coil circuit)
70 — Dark Blue/Pink -------- 85 ----- PCM grounds this to energize relay and turn on relay & fan (coil)
73 ---- Gray -------------------- 87 ---- Battery voltage at all times (NO switch)
71 — Yellow --------------------30 ---- Battery voltage when relay is turned on, connects to fan motor (NO)

12 volt relays use a standard pin number nomenclature. I recall running into these pin numbers before; for example when I installed a relay so I could have a push button start on my Corolla.

85 Coil
86 Coil
87 Normally Open (NO)
87a Normally Closed (NC) - not present on 4 pin relays
30 Common connection to NO & NC terminals

Perfect, thanks! That’s correct on my relay and 87a is the unused center. I’ll test 69/70 tomorrow when I have daylight and no rain/snow. I tried a second computer and got the same p0481 so I’m betting on the ground on the db/pk. Could I also test by checking for continuity between db/pk and a chassis ground with the PCM unplugged? What is my next move if it’s a short in the db/pk chassis ground?

You’ll have to trace out where the short is occurring

Is it occurring?

  • inside the relay box (the thing you plug the relay into)
  • on the wire between the relay box and the pcm
  • on the pcm circuit board

First thing to do then is disconnect the blue/pink wire between the box and the pcm, and check if pin 85(70) at the relay box is connected to ground or not. If it is, there’s a short circuit inside the relay box. If it is not there, use the same method to figure out which segment of the circuit it is occurring.

Thank you very much, I’ll revisit it tomorrow and get what I can done between weather and work and post back.