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97 Neon Code 35 Radiator Fan


Louseman
01-03-2004, 11:09 AM
Any techniques for troubleshooting the radiator fan relay circuit for a neon? Replaced the relay (strut mounted, not in power distribution center). Get a code 35 on the check engine light, as the radiator fan
does not run when A/C is engaged. Fuse 10 is fine. Does the PCM only
monitor the low current side of the circuit?

PS: If purchasing the relay from a dealer, tell them it is for a Caravan, same part. Recall pricing from the dealer.

Louseman
01-04-2004, 10:27 AM
OK, got this fixed with this info from another board:

Radiator Fan Control Module - PCM Output

The radiator fan runs when coolant temperature and A/C system pressure demand cooling. The radiator fan circuit contains a Pulse Width Module (PWM) this is shown on the wiring as the Solid State Fan Relay.

A 5 volt signal is supplied to the PWM. The PCM provides a pulsed ground for the PWM. Depending upon the amount of pulse on time, the PWM puts out a proportional voltage to the fan motor at the lower speed. For instance, if the on time is 30 percent , then the voltage to the fan motor will be 3.6 volts .

When engine coolant reaches approximately 99°C (210°F) the PCM grounds the PWM relay. When the PCM grounds the relay it operates at a 30% duty cycle and immediately ramps up to 100% duty cycle. The PCM de-energizes the PWM relay when coolant temperature drops to approximately 93°C (199°F) .

Also, when the air conditioning pressure switch closes, the PCM grounds the PWM. The air conditioning switch closes at 285 psi ±10 psi . When air conditioning pressure drops approximately 40 psi , the pressure switch opens and the fan turns off.

The PWM relay is located on the left front inner frame just behind the radiator.


And the following.....

The relay power (pin 4) is protected by a 30A fuse (#5) on circuit A16 in the PDC, always hot to the relay.

The return side of the relay is controlled by the PCM, which connects it to ground a % of the time based on the need for cooling, at pin 18 of the PCM connector. This is a light green wire at the PCM, Dark green at pin 2 on the relay.

The relay is also grounded at pin 1. This goes to the same ground as the fans, but through a splice in the chain.


My problem was that the light green wire from pin 18 at the PCM
was broken before the connector attached below the power block.
Soldered in a splice, and all is well. Found it using continuity checks
for all of the wires, after knowing the color scheme/connector positions.

Hope this info helps someone. The moral is: Get the real FSM's!

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