Overheating, Radiator Fans not turning on
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ChippaT
- SE Member

- Posts: 13
- Joined: Tue Jan 19, 2021 3:30 pm
- Year and Trim: 2002 Pontiac Bonneville SLE
Miles: 169,XXX
Overheating, Radiator Fans not turning on
When driving around car wont go over 200 degrees, at a stand still will heat up to 210+. Whenever it reached this temperature I would shut it off and let it cool down. AC does not work nor does it turn on the fans. Unplugging temperature sensor makes fans run by default. Ive swapped around the relays with a new one as well as testing the old ones by swapping with ignition relay. Will be swapping coolant temperature sensor tonight.
- harofreak00
- Administrator

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- Year and Trim: 2004 GXP - plus a handful of other Bonnevilles
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Re: Overheating, Radiator Fans not turning on
According to the FSM, the fans shouldn't come on until 223°F.
Cooling System Description and Operation
Cooling Fan Control
The engine cooling fan system consists of two electrical cooling fans and three fan relays. The relays are arranged in a series/parallel configuration that allows the powertrain control module (PCM) to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the underhood fuse block. The ground path is provided at G103.
During low speed operation, the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the cooling fan 1 relay coil, closes the relay contacts, and supplies battery positive voltage from the cool fan 1 fuse through the cooling fan motor supply voltage circuit to the right cooling fan. The ground path for the right cooling fan is through the cooling fan s/p relay and the left cooling fan. The result is a series circuit with both fans running at low speed.
During high speed operation the PCM supplies the ground path for the cooling fan 1 relay through the low speed cooling fan relay control circuit. After a 3-second delay, the PCM supplies a ground path for the cooling fan 2 relay and the cooling fan s/p relay through the high speed cooling fan relay control circuit. This energizes the cooling fan s/p relay coil, closes the relay contacts, and provides a ground path for the right cooling fan. At the same time the cooling fan 2 relay coil is energized closing the relay contacts and provides battery positive voltage from the cool fan 2 fuse on the cooling fan motor supply voltage circuit to the left cooling fan. During high speed fan operation, both engine cooling fans have there own ground path. The result is a parallel circuit with both fans running at high speed.
The PCM commands Low Speed Fans on under the following conditions:
Engine coolant temperature exceeds approximately 106°C (223°F).
A/C refrigerant pressure exceeds 1310 kPa (190 psi).
After the vehicle is shut off if the engine coolant temperature at key-off is greater than 118°C (244°F) and system voltage is more than 12 volts. The fans will stay on for approximately 3 minutes.
The PCM commands High Speed Fans on under the following conditions:
Engine coolant temperature reaches 112°C (234°F).
A/C refrigerant pressure exceeds 1634 kPa (237 psi).
When certain DTCs set.
Andrew - owner/operator of Bonnevilles Unlimited

2004 Bonneville GXP | 60k | White Gold Tricoat | custom built supercharged 3800 hot rod | garage queen
1997 Corvette | 57k | Silver Metallic | Z06 wheels | Date-night Hauler/Parts runner
2014 Town & Country Limited | Cashmere Pearl | 115k | Family Hauler
2002 Ram 1500 Quad Cab Sport | Black| 280k | Official Bonneville Hauler

2004 Bonneville GXP | 60k | White Gold Tricoat | custom built supercharged 3800 hot rod | garage queen
1997 Corvette | 57k | Silver Metallic | Z06 wheels | Date-night Hauler/Parts runner
2014 Town & Country Limited | Cashmere Pearl | 115k | Family Hauler
2002 Ram 1500 Quad Cab Sport | Black| 280k | Official Bonneville Hauler
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ChippaT
- SE Member

- Posts: 13
- Joined: Tue Jan 19, 2021 3:30 pm
- Year and Trim: 2002 Pontiac Bonneville SLE
Miles: 169,XXX
Re: Overheating, Radiator Fans not turning on
A/C refrigerant pressure was low so the compressor wouldnt kick on nor the fans. Charged it up and everything works as should. Probably have a leak I need to find.
- nos4blood70
- Certified Bonneville Nut

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- Year and Trim: 2003 SLE
- Location: Chicago, IL
Re: Overheating, Radiator Fans not turning on
These cars run pretty warm from the factory, so your fan behavior is normal. Sounds like you need to get some UV dye in there and poke around at night with a light.


