Procedure to by-pass engine coolant fan relay?
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Joined: Dec 1969
Posts: 27,730
From: Little Rock, AR
It is with the fan relay #1 indicated as on (as the Datamaster program specifies it is signaling FR#1 to come on at 226F. The key is out of the ignition.
I'm probing the Fan relay side on C100 "J" with ignition off. I hold the lead on that probe and the other lead on the car chassis.
The meter is set to 2K reading Ohms resistance. The reading when I hold it on the D2 position (for FR#1 and the car chassis) is "1" or open/shorted (?). This is of course with the C100 still connected to the PCM.
And on c100 "J" is also reading "1" when I probe the FR side of the connector (which I guess makes sense if the fan relay has been removed...should I be checking the ground from the PCM side at C100?)
I think I'm getting close to finding the problem...
I'm probing the Fan relay side on C100 "J" with ignition off. I hold the lead on that probe and the other lead on the car chassis.
The meter is set to 2K reading Ohms resistance. The reading when I hold it on the D2 position (for FR#1 and the car chassis) is "1" or open/shorted (?). This is of course with the C100 still connected to the PCM.
And on c100 "J" is also reading "1" when I probe the FR side of the connector (which I guess makes sense if the fan relay has been removed...should I be checking the ground from the PCM side at C100?)
I think I'm getting close to finding the problem...
You never said what your reading is with the leads touched together. That will help me tell if your what your reading of "1" is.
You can also put one end of your meter at D2 and the other end at cavity J toward the relay. You should get little or no resistance (should be the same reading as if you touched the leads together).
Last edited by shoebox; Sep 2, 2007 at 01:29 PM.
Thread Starter
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Joined: Jun 2004
Posts: 65
Ahh, that makes complete sense that the PCM has to be commanding the ground information to the relay for me to check it. So I need to run the car and bring it up to the 226K then the FR#1 should be ready to check to see if the ground info is reaching D2.
The reading of the DVM at 2K with the leads touched together is zero.
I'll try the above and let you know.
The reading of the DVM at 2K with the leads touched together is zero.
I'll try the above and let you know.
Thread Starter
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Joined: Jun 2004
Posts: 65
Ok, last night I wiggled the back side of the D2 connector under the relay/fuse box...
Today, I ran the car until the PCM sent a ground to D2 (226F)...I placed the DVM on 2K and read the ohms from D2...it read -0.022...then miraculously the low speed came on when I put the relay back in ??! I waited until the engine hit 235K and then the fans kicked into high.
BUT this still does not solve my problem as over the last few weeks when I drove to work and the temp got to 226F plus...the low oil light would come on the dash guage and the oil pressure would read only about 25 KPa. Today when the fans came on this problem still happened and the 77 DTC came up on DM...The oil level is normal...
What also does not make sense is my fans would always come on at around 180F before and the temp would stay in this low range even in city traffic...where the temp guage goes up to now was not what happened before...but from your website Shoebox it indicates the fans will come on at 226F low and 235F high.
What would we be dealing with...? There is something wrong...should I remove the PCM fuse to reset the codes and see if it stills happens...or?
Today, I ran the car until the PCM sent a ground to D2 (226F)...I placed the DVM on 2K and read the ohms from D2...it read -0.022...then miraculously the low speed came on when I put the relay back in ??! I waited until the engine hit 235K and then the fans kicked into high.
BUT this still does not solve my problem as over the last few weeks when I drove to work and the temp got to 226F plus...the low oil light would come on the dash guage and the oil pressure would read only about 25 KPa. Today when the fans came on this problem still happened and the 77 DTC came up on DM...The oil level is normal...
What also does not make sense is my fans would always come on at around 180F before and the temp would stay in this low range even in city traffic...where the temp guage goes up to now was not what happened before...but from your website Shoebox it indicates the fans will come on at 226F low and 235F high.
What would we be dealing with...? There is something wrong...should I remove the PCM fuse to reset the codes and see if it stills happens...or?
Registered User
Joined: Dec 1969
Posts: 27,730
From: Little Rock, AR
Sounds like it is working right some of the time, now. Maybe a loose connection or one of the relays is bad? If you never had any programming done to the fans, then they should come on at 226°.
Thread Starter
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Joined: Jun 2004
Posts: 65
SOLVED THE PROBLEM!!!
After learning a tonne of information about the electrical system and PCM. Then building the converter for the PC and Datamaster scan...(thank you to Andrew at AKM cables for the thorough schematic and parts list from his website so I could build the converter from scratch...it was fun).
The electrical system was ok after scanning the engine/PCM. But the car was still overheating...and the engine light was actually the low coolant guage...I checked the thermostat...ran the car until the temp ran up to the 226F range and then I felt the upper radiator coolant line...which should be HOT at that temp...but it wasn't...this is when I figured out the problem was the thermostat! I changed the 160 hypertech to the original stock I had kept from three years ago...NOW it runs like new, temp normal...EVERYTHING IS GOOD! I don't know why the hypertech only lasted three years...
THANK YOU to everyone that helped out...ESPECIALLY SHOEBOX!
After learning a tonne of information about the electrical system and PCM. Then building the converter for the PC and Datamaster scan...(thank you to Andrew at AKM cables for the thorough schematic and parts list from his website so I could build the converter from scratch...it was fun).
The electrical system was ok after scanning the engine/PCM. But the car was still overheating...and the engine light was actually the low coolant guage...I checked the thermostat...ran the car until the temp ran up to the 226F range and then I felt the upper radiator coolant line...which should be HOT at that temp...but it wasn't...this is when I figured out the problem was the thermostat! I changed the 160 hypertech to the original stock I had kept from three years ago...NOW it runs like new, temp normal...EVERYTHING IS GOOD! I don't know why the hypertech only lasted three years...
THANK YOU to everyone that helped out...ESPECIALLY SHOEBOX!
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