I rebuilt an automatic transmission for an 84 Sentra and reinstalled. The car hasn't run since due to no spark. Here are a few troubleshooting updates:
- The LED's on the ECU are dead. Both red and green... they never light.
- According to the Haynes book, there is a 20 amp fuse in circuit. I tested all 20 amp fuses and they check ok. there are no fuses under the hood.
- I tested the coil and I get 12v through it with the key on.
- There is only one wiring harness to the tranny, and all 4 posts are clean and making good connection.
It seems to me that troubleshooting the rest of the ignition components is worthless if there is no ECU. Is there something in the wiring with a tranny rebuild/installation that I am overlooking? Spark was fine before I pulled the transmission.
Well I quit looking at plugs, power transistor, and everything else for now (although I tested all of that and they all check ok). I figured that until I get LEDs on the ECU, there isn't any sense in looking any further. I haven't checked the ECC relay yet, but with a tranny rebuild, the ECC relay seems like an odd place to look for the trouble. I'm wondering if I am overlooking something with the Tranny re-installation? I thinking that if there is no ECU, there is no spark...
Here is an update (still no LEDs on the ECU):
-The harness to the transmission has 4 posts. 2 ground and 2 12v. With the key on, I get 12v to both of the hot posts. I'm thinking that the tranny is NOT the problem.
- I double-checked, and all fuses are good. I also checked the two relays in the fuse box and they both check ok.
- I pulled the ECC relay and found good 12v and ground with the key on. I shorted accross the relay with a wire (to bypass the relay). Still no ECU LEDs. I'm thinking that I DON"T have a relay problem.
So the coil, power tranformer, relays, harness to the tranny, and fuses have all been checked. What am I missing? I still think that with no ECU LEDs, i shouldn't expect spark at the coil. Am I on the right track?
Here is an update (still no LEDs on the ECU):
-The harness to the transmission has 4 posts. 2 ground and 2 12v. With the key on, I get 12v to both of the hot posts. I'm thinking that the tranny is NOT the problem.
- I double-checked, and all fuses are good. I also checked the two relays in the fuse box and they both check ok.
- I pulled the ECC relay and found good 12v and ground with the key on. I shorted accross the relay with a wire (to bypass the relay). Still no ECU LEDs. I'm thinking that I DON"T have a relay problem.
So the coil, power tranformer, relays, harness to the tranny, and fuses have all been checked. What am I missing? I still think that with no ECU LEDs, i shouldn't expect spark at the coil. Am I on the right track?
I bet I know what's wrong with it. I actually posted this info a few years ago. I'm sure a search would unearth it.
In a nutshell, your transmission has nothing to do with it. If you remove the coolant overflow bottle, and the black plastic shield behind it, you will expose the ECCS relay. Look at the yellow [power] wire going into the relay connector. If it isn't already rotted off, then pull on it gently and it will fall off. You can fix this by cutting off the corroded relay connector and crimping on for insulated spade connectors[from any auto store]. If the relay itself is so corroded it can't be cleaned up, replace it. Otherwise, make sure to connect the individual four new connectors in the right order to the relay and start her up.
If I am right [and I'll bet I am] donations are gladly accepted in my Paypal account.
Thanks for the info. I checked the yellow wire that you referred to... it appears to be attached to the coupler very well. Short of cutting it off, it won't be falling off any time soon...
Could corrosion still be the problem? Should I go ahead and cut the wires off and spade-tip them, then plug directly into the relay? Should I go ahead and replace the relay while I'm at it?
Could corrosion still be the problem? Should I go ahead and cut the wires off and spade-tip them, then plug directly into the relay? Should I go ahead and replace the relay while I'm at it?
Pull it apart. If it looks good, you've got something else wrong. Maybe you did screw up some wiring when you changed the trans. That I would not know. Check to make sure your ecu didn't get wet at any time either. Open it up and look for corrosion or water damage.
check the fuseable links by the battery, ensure that you did not disturb any grounds or wires when you did the R&R also look at any wiring connectors that you could have confused I don't know how long the tranny was out but you could have switched a pair. Check for power to the ECU itself and also check for a ground at that. if all that passes get your hands on a tester ECU either from a parts car a freinds car or the scrap yard and see what hapens. if from the scrap yard try not to pay to much since it may not work.
Mille wins the prize... sort of. I finally got a look a the wiring diagram for the ignition system. The ECC relay was pulling 12v from one post... I should have seen 12v from 2 posts, one always hot, one hot with the key turned on. The "always hot" lead was dead.
That lead me to the fuseable link, which was gone. The owner before me replaced the battery cables and tore the fuseable links out and installed wiring harnesses and did a poor job installing the harnesses. When I removed the electrical tape, the leads to the ECC relay fell out in my hand. There is a yellow wire at the point where there should have been a fuseable link. I metered for resistance between the connector behind the battery and the yellow lead at the ECC relay and their was no resistance... good to go. I reconnected all of the wiring that fell apart when I removed the tape (everything connected to the + side of the battery except the starter). Two posts now had 12v at the ECC relay.
Put everything back in and turned the key... son of a bitch started right up (made one hellava lot of noice until I got the fluids topped off).
No worries with the tranny rebuild, I ran it through the gears while it was still on blocks. Everything looks and sounds good. I'll have it on the road tomorrow. I'll keep you posted...
Last edited by rlapix : Dec 22nd, 2004 at 01:04 AM.
I rebuilt an automatic transmission for an 84 Sentra and reinstalled. The car hasn't run since due to no spark. Here are a few troubleshooting updates:
- The LED's on the ECU are dead. Both red and green... they never light.
- According to the Haynes book, there is a 20 amp fuse in circuit. I tested all 20 amp fuses and they check ok. there are no fuses under the hood.
- I tested the coil and I get 12v through it with the key on.
- There is only one wiring harness to the tranny, and all 4 posts are clean and making good connection.
It seems to me that troubleshooting the rest of the ignition components is worthless if there is no ECU. Is there something in the wiring with a tranny rebuild/installation that I am overlooking? Spark was fine before I pulled the transmission.
still troubleshooting an 84 Sentra ECU
I actually posted this info a few years ago. I'm sure a search would unearth it. 
Linear Mode
