nikosgod

Hello i have 1998 Corvette with 116K miles, AC doesn't work, so its never on. Last repair was putting in a new waterpump and thermostat. Now both cooling fans are always on high speed after about 10 minutes when the vehicle is warming up. The temp gauge reaches around 180F when the fans are on high.

I took it back to my mechanic, he tested both fan speeds independently, low speed worked fine and high speed fan worked fine too.

So he recommended taking out the pcm and replacing it with a new/refurbished unit and get it reflashed by gm. Then it should fix the problem, so he says.


These are the dic codes that show up.

10-PCM
P0135 C (HO2S Heater Circuit Bank 1 Sensor 1)
P0155 C (HO2S Heater Circuit Bank 2 Sensor 1)
P0410 H C (AIR System)

60-IPC
B1543 H (Oil Temperature Circuit Open)


Any advice would be appreciated.
Thanks,
Nick

dgrant3830

I really can't answer this one for you although this will provide a TTT for someone else who might be able to assist better. I'm thinking that you need to have it to a dealer or someone with a Tech2 who is familiar with Corvettes. If the radiator cooling fans are on at high-speed, then possibly one of the three relays is stuck closed or the coolant temp sensor is having issues.

lionelhutz

A TechII should be capable of turning the fans on and off. So, 10 minutes with a TechII will tell you if it's the computer or the wiring as well as telling you what the computer thinks the engine temperature is. I somewhat suspect you have air in the cooling system.

Peter

Bill Dearborn

How do you know the fans are on high speed? Just because they are both on doesn't mean they are running at high speed. You said the mechanic found the high speed fan (not fans, highlighted quote above) worked fine. If all he was doing was checking the fans independently of each other he didn't understand the circuit.

When the fans are turned on in slow speed mode they both run in a series circuit which cuts the voltage across each one of them in half. On the high speed setting the relays change the circuit so both fans are running in a parallel circuit which gives full battery voltage to both of them and they run twice as fast.

Before playing with the PCM check the most obvious failures first. Relay's are notoriously unreliable compared to solid state electronic circuits so make sure the relays are working correctly. You can quickly make up a little test circuit with a toggle switch and a couple of wires. Connect the wires to each end of the switch and then connect the opposite end of one to a good ground. Then connect the other end to pin E2 of relay 45 and close the toggle switch. This should turn on both fans in low speed operation. With another toggle switch ground pin A10 of relay 44 or pin E10 of relay 43. This will turn both fans onto high speed.

Here is the schematic:


Bill

nikosgod

Mechanic used a scan tool, not exactly certain if it was a tech II, turned on the low speed fan operation then the high speed fan. Told me that when the temperature reached 84C/183F the fans would turn on high.

When i start up the vehicle, even in the bitter cold temperatures in January, about 5 minutes or so, the fans will turn on, then another 5 mintues the high fans turn on, just from sitting, not driving it. They sound like a jet engine, very loud and annoying.

Assuming that fans and wiring are good, would the pcm (what ever commands the fans) need to be adjusted so they start at a higher temp? Ever since the waterpump/thermostat installation this issue hasn't stopped.

Thanks again for all your responses,
Nick

Rick Galindo

so did you find the problem . I to change the water pump and thermostat and know a/c don't work one of cooling fans only runs slow speed and at start up I get a charging fault . I give it gas and it turns off .