# 04 Nissan sentra won't start. Bad ECM?
**URL:** https://boards.straightdope.com/t/04-nissan-sentra-wont-start-bad-ecm/590103
**Category:** Factual Questions
**Created:** [July 23, 2011, 7:57pm UTC](https://boards.straightdope.com/t/04-nissan-sentra-wont-start-bad-ecm/590103 "2011-07-23T19:57:51Z")
**Posts on this page:** 14
**Page:** 1
### Author:  [@Willcross](https://boards.straightdope.com/u/Willcross)
#### Post date: [July 23, 2011, 7:57pm UTC](https://boards.straightdope.com/t/04-nissan-sentra-wont-start-bad-ecm/590103/1 "2011-07-23T19:57:51Z")
My fiance’s 04 nissan sentra 1.8 died on the road yesterday. We had it towed back to the house and I’m looking at it now.
The first thing I noticed is the fuel pump is not coming on at all. I replaced the relay and checked the fuse. I brought my multimeter home from work, and the pump doesn’t seem to be getting power. I jumped power to the pump straight from the battery and it comes on then; so it seems the pump is good.
I disconnected the fuel line going into the rail and jumped the pump again. Fuel poured out of the line. So i’m guessing that eliminates restrictions in the fuel system.
In conclusion, for some reason the fuel pump is not getting power. I read online that the service engine soon light should come on for a few seconds with the key on. This is not happening now, but I never noticed if it used to or not.
Right now i’m leaning towards a problem with the ecm, either it’s faulty or has a poor ground or power wire. Can ECMS on this model sentra be interchanged or are they mated to the vehicle by vin? Is the junkyard an option if this is the case?
Does anyone know where the fuel pump grounds by chance? Just realized it could be a poor ground.
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### Author:  [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)
#### Post date: [July 23, 2011, 9:02pm UTC](https://boards.straightdope.com/t/04-nissan-sentra-wont-start-bad-ecm/590103/2 "2011-07-23T21:02:03Z")
Fuel pumps are usually inside the gas tank itself so a bad ground is unlikely (think TWA 800!)
Long shot but-
You say the **CHECK ENGINE** light is \*\*NOT \*\*lighting when you turn the ignition on? A car won’t run if you remove that bulb so if it burnt out it might have the same effect. Be an easy, cheap fix anyway!
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### Author:  [@Willcross](https://boards.straightdope.com/u/Willcross)
#### Post date: [July 23, 2011, 9:06pm UTC](https://boards.straightdope.com/t/04-nissan-sentra-wont-start-bad-ecm/590103/3 "2011-07-23T21:06:14Z")
Yeah I just remembered I checked continuity between the ground wire in the fuel pump harness and the door striker and it was good. So prolly not a ground issue. Gonna go outside to check if its a physical and replaceable bulb in the cluster or if its a nonservicable type thing.
I’m a VW tech with a year of experience so i’m familiar with cars but not nissan in particular.
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### Author:  [@Gary\_T](https://boards.straightdope.com/u/Gary_T)
#### Post date: [July 23, 2011, 9:12pm UTC](https://boards.straightdope.com/t/04-nissan-sentra-wont-start-bad-ecm/590103/4 "2011-07-23T21:12:28Z")
> [@Willcross](#):
>
> I jumped power to the pump straight from the battery and it comes on then; so it seems the pump is good.
>
> Does anyone know where the fuel pump grounds by chance? Just realized it could be a poor ground.
If it runs when you jump power to it then it has an adequate ground. If you weren’t also jumping the ground to it, how could it be a bad ground?
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### Author:  [@Gary\_T](https://boards.straightdope.com/u/Gary_T)
#### Post date: [July 23, 2011, 9:16pm UTC](https://boards.straightdope.com/t/04-nissan-sentra-wont-start-bad-ecm/590103/5 "2011-07-23T21:16:24Z")
> [@Hail\_Ants](#):
>
> Fuel pumps are usually inside the gas tank itself so a bad ground is unlikely (think TWA 800!)
Typically the fuel pump module is electrically isolated from the tank itself (which may be plastic anyway) and the ground is supplied by a separate wire just like the power is.
> [@](#):
>
> Long shot but-
> You say the **CHECK ENGINE** light is \*\*NOT \*\*lighting when you turn the ignition on? A car won’t run if you remove that bulb so if it burnt out it might have the same effect. Be an easy, cheap fix anyway!
Never heard of that in over 35 years repairing cars professionally, and have personally observed some vehicles that ran even though the bulb was burnt out. Methinks you have been snookered by an unreliable source.
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### Author:  [@Willcross](https://boards.straightdope.com/u/Willcross)
#### Post date: [July 23, 2011, 9:27pm UTC](https://boards.straightdope.com/t/04-nissan-sentra-wont-start-bad-ecm/590103/6 "2011-07-23T21:27:52Z")
> [@Gary\_T](#):
>
> If it runs when you jump power to it then it has an adequate ground. If you weren’t also jumping the ground to it, how could it be a bad ground?
I was actually also jumping ground to it. My jumper wires weren’t long enough to reach the engine compartment so I removed the battery and sat it next to the car and jumped power and ground.
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### Author:  [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)
#### Post date: [July 23, 2011, 9:32pm UTC](https://boards.straightdope.com/t/04-nissan-sentra-wont-start-bad-ecm/590103/7 "2011-07-23T21:32:05Z")
I would definitely double and triple check the ECM fuse before you start really delving any deeper. Like actually check it for continuity. If the bulb isn’t coming on (and isn’t burnt out) either the ECU is bad or isn’t getting power. I’ve also never heard the bulb thing.
As for the part, they’re not attached to an exact VIN but unless you want to pay the dealer big bucks to flash the new ECU to your car’s specifications, you should try to find one with the exact same options. Easier said than done though, since that includes stuff like whether it has cruise control, a security system or California emissions. The used parts site [Car-part.com](http://Car-part.com) shows no less than 21 ECU options for '04 Sentras! Further complicating things, if you buy a new one there seems to be two different actual ECU’s, requiring you to read the part number off the old one.
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### Author:  [@jz78817](https://boards.straightdope.com/u/jz78817)
#### Post date: [July 23, 2011, 10:09pm UTC](https://boards.straightdope.com/t/04-nissan-sentra-wont-start-bad-ecm/590103/8 "2011-07-23T22:09:41Z")
> [@Gary\_T](#):
>
> Typically the fuel pump module is electrically isolated from the tank itself (which may be plastic anyway) and the ground is supplied by a separate wire just like the power is.
nevermind the fact that there’s no (or at worst not enough) oxygen in the tank for the gas vapors to ignite.
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### Author:  [@Willcross](https://boards.straightdope.com/u/Willcross)
#### Post date: [July 23, 2011, 11:07pm UTC](https://boards.straightdope.com/t/04-nissan-sentra-wont-start-bad-ecm/590103/9 "2011-07-23T23:07:12Z")
I checked the ecm fuses and they were good, no high resistance or anything. Gonna look at mitchell on demand at work monday. Guess i"ll pull a wiring diagram to check for powers and grounds on the ecm. Thanks for all the advice
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### Author:  [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)
#### Post date: [July 24, 2011, 1:58pm UTC](https://boards.straightdope.com/t/04-nissan-sentra-wont-start-bad-ecm/590103/10 "2011-07-24T13:58:51Z")
They may be able to tell the difference between a burnt and a missing bulb but sometime in the late 80s early 90s manufacturers starting making them so they wouldn’t work if there was no bulb.
For those that don’t know, the CHECK ENGINE light simply means the car’s computer is sending an error code of some kind, could be minor or major. So it became common practice for used car dealers to just pull the indicator bulbs to ‘fix’ this.
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### Author:  [@Gary\_T](https://boards.straightdope.com/u/Gary_T)
#### Post date: [July 25, 2011, 4:31am UTC](https://boards.straightdope.com/t/04-nissan-sentra-wont-start-bad-ecm/590103/11 "2011-07-25T04:31:09Z")
> [@Hail\_Ants](#):
>
> They may be able to tell the difference between a burnt[-out] and a missing bulb…
No, either there’s resistance/voltage drop or there’s not.
> [@](#):
>
> …sometime in the late 80s early 90s manufacturers starting making them so they wouldn’t work if there was no bulb.
In polling my colleagues, I find some remember this to be the case for (at least some) GM models during that timeframe. Come 1996 and OBDII systems, apparently it’s not the case for any manufacturer.
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### Author:  [@jz78817](https://boards.straightdope.com/u/jz78817)
#### Post date: [July 25, 2011, 3:01pm UTC](https://boards.straightdope.com/t/04-nissan-sentra-wont-start-bad-ecm/590103/12 "2011-07-25T15:01:57Z")
> [@](#):
>
> For those that don’t know, the CHECK ENGINE light simply means the car’s computer is sending an error code of some kind, could be minor or major. So it became common practice for used car dealers to just pull the indicator bulbs to ‘fix’ this.
A steady CEL means the PCM has logged a hard fault which can cause the car’s emissions to rise above specification. A flashing CEL means there is a repeated hard fault (frequently a misfire) which can cause damage to the catalyst. OBD II specifies what faults must light the CEL. I _think_ manufacturers can use it for more than that, but I’m not 100% sure.
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### Author:  [@Leaffan](https://boards.straightdope.com/u/Leaffan)
#### Post date: [July 25, 2011, 3:18pm UTC](https://boards.straightdope.com/t/04-nissan-sentra-wont-start-bad-ecm/590103/13 "2011-07-25T15:18:54Z")
No one has mentioned the emergency shut-off switch for the fuel pump yet?
Has it been triggered or disabled somehow?
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### Author:  [@Rick](https://boards.straightdope.com/u/Rick)
#### Post date: [July 25, 2011, 3:40pm UTC](https://boards.straightdope.com/t/04-nissan-sentra-wont-start-bad-ecm/590103/14 "2011-07-25T15:40:09Z")
Does the car have spark? On many systems the ECM does not turn on the pump until it sees an ignition signal.
It would be a shame to put a new ECM in for a bad RPM sensor.