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Thread: Is there an easy way to test the relays in the power distribution box?

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    wh23g3g's Avatar
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    Default Is there an easy way to test the relays in the power distribution box?

    I had that pending code P0711 come up and now it's set a hard code. Trans Temp and O/D off light are on all the time now. I know it's not too hot because it's right when I start it up. I was thinking it had something to do with that inline fuse on the violet wire coming from the PCM that I noticed. When I was driving my 99 today to the park today after finishing the underhood detailing job I've been working on for two weeks it throw a code on the way there. It went off half way there and then on the way back it came on again. It never went back off even when I shut the truck off and restarted it. However, my scanner somehow picked up the pending code for the transmission but it won't read a transmission hard code. So I assume it's still the P0711. I'm wondering if something I've overlooked the whole time I've had this truck is to replace the 20+ year old transmission control relay. It's the original one. Actually looks like all the fuses and relays are original except the starter because mine actually would try to start on it's own a few years ago. Is there any easy way to check these? I could just swap them or should I replace all of them?

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    Quote Originally Posted by wh23g3g View Post
    I had that pending code P0711 come up and now it's set a hard code. Trans Temp and O/D off light are on all the time now. I know it's not too hot because it's right when I start it up. I was thinking it had something to do with that inline fuse on the violet wire coming from the PCM that I noticed. When I was driving my 99 today to the park today after finishing the underhood detailing job I've been working on for two weeks it throw a code on the way there. It went off half way there and then on the way back it came on again. It never went back off even when I shut the truck off and restarted it. However, my scanner somehow picked up the pending code for the transmission but it won't read a transmission hard code. So I assume it's still the P0711. I'm wondering if something I've overlooked the whole time I've had this truck is to replace the 20+ year old transmission control relay. It's the original one. Actually looks like all the fuses and relays are original except the starter because mine actually would try to start on it's own a few years ago. Is there any easy way to check these? I could just swap them or should I replace all of them?
    Yes. There are several ways.
    Every relay has a power input and out put side. There should be a diagram on the outside of the relay to show which is which. Get a couple alligator clips attached to either your car battery or a cordless tool battery and being aware of ground and hot side, attach the clips to the relay input side and you should hear a "click".
    You can then put an ohm meter on the output side and you should have no resistance because hearing the "click" is not always enough if something is lodged between the relay contacts. You can also pry open the relay with a screw driver and after attaching power, see if your contact is closing.

    Another way is to simply switch relays with a similar one within the box and see if that item works with the suspect relay.

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    wh23g3g's Avatar
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    It's definitely not the relay. I put a brand new one in that I had and the trans temp and OD off light are still on. Plus the battery had been disconnected for a couple weeks too while I was doing some underhood detailing.

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