2G P1500 and SRS mistake 😭

[Taskin]

Hi, thanks for having me here. My English isn't great, but I've been an Eclipse fanatic for 25 years.

Regarding my problem:
I'm getting error code P1500 on my OBD scanner:
Vehicle Speed Sensor Intermittent
General alternator "FR" terminal circuit fault; Vehicle Speed Sensor Intermittent. Also, the SRS light on my dashboard is on. I installed a new alternator, but it didn't help—the errors are still there.

What should I do next? Does anyone have any ideas? I’d really appreciate it.

1997 Eclipse Spyder GS (4G64).

 

[Vladimir]

What's your output voltage from the alternator to battery?

Make sure there is no corrosion in the alternator 4 pin connector. Make sure there is no open circuit or excessive resistance on the two wires circled. I would start there. Before checking the PCM.

Not sure about the SRS light, there is not enough details provided. But If the alternator is not charging and voltages are low, some lights can turn ON.

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[Taskin]

What's your output voltage from the alternator to battery?

Make sure there is no corrosion in the alternator 4 pin connector. Make sure there is no open circuit or excessive resistance on the two wires circled. I would start there. Before checking the PCM.

Not sure about the SRS light, there is not enough details provided. But If the alternator is not charging and voltages are low, some lights can turn ON.

Thanks Vladimir, I'll check things out and get back to you.

 

[luv2rallye]

Make sure your dash "Charge" light (aka "alt" lamp) is working (should come on when you first turn the key to on but engine not running yet). It provides necessary voltage to the Alt's field coil to work (also needed for the "FR" terminal).

For SRS light you should check its red connector behind the glove box door which can intermittently make a poor connection over time causing the light to come on. Just unplug and re-plug it (while keeping your head away from the airbag there).
See: https://www.dsmtuners.com/threads/glove-box-light.435692/#post-153493943

 

[Taskin]

Make sure your dash "Charge" light (aka "alt" lamp) is working (should come on when you first turn the key to on but engine not running yet). It provides necessary voltage to the Alt's field coil to work (also needed for the "FR" terminal).

For SRS light you should check its red connector behind the glove box door which can intermittently make a poor connection over time causing the light to come on. Just unplug and re-plug it (while keeping your head away from the airbag there).
See: https://www.dsmtuners.com/threads/glove-box-light.435692/#post-153493943

Okay, thanks—I'll check that too. It's 10 a.m. in Germany right now. I need to wake up first; I need about ten coffees.

 

[luv2rallye]

The "Generator Relay" (which is just a diode in series with a resistor) provides a backup (for alt field coil voltage) should the Charge light not work. If it or it's wire to the alt got shorted to ground, that also would keep the alt from working and make the Charge light go on (assuming all wiring is good). Make sure you don't have 0 volts there (which is also alt's "L" terminal) when the key is "ON". Note that wire is black/yellow to the alt (alt is shown as generator) but blue to the Charge light's negative side (Charge light's positive side goes to ignition switch).

 

[Taskin]

What's your output voltage from the alternator to battery?

Make sure there is no corrosion in the alternator 4 pin connector. Make sure there is no open circuit or excessive resistance on the two wires circled. I would start there. Before checking the PCM.

Not sure about the SRS light, there is not enough details provided. But If the alternator is not charging and voltages are low, some lights can turn ON.

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Hello again. Here are the readings from today:

Battery: 13.1 V

Alternator connector (ignition in ON position):

Green wire: 1.50 V
Black/Yellow wire: 12.0 V
Red wire: 12.8 V
White wire: 0 V

There is continuity between ECU pin 41 and the white wire at the alternator connector (it beeps).

ECU pin 41: 4.9 V

Thick cable (with red cap) at the alternator: 12.8 V

SRS connector (passenger side) was unplugged and cleaned with contact spray.

My instrument cluster doesn't have an "ALT" light; unfortunately, it's not equipped with one.

I'm not exactly an expert on automotive electronics, but perhaps the data I've gathered will help us.

Maybe the car's sound system caused the damage—I have no idea.

 

[Taskin]

The "Generator Relay" (which is just a diode in series with a resistor) provides a backup (for alt field coil voltage) should the Charge light not work. If it or it's wire to the alt got shorted to ground, that also would keep the alt from working and make the Charge light go on (assuming all wiring is good). Make sure you don't have 0 volts there (which is also alt's "L" terminal) when the key is "ON". Note that wire is black/yellow to the alt (alt is shown as generator) but blue to the Charge light's negative side (Charge light's positive side goes to ignition switch).

Hello again. Here are the readings from today:

Battery: 13.1 V

Alternator connector (ignition in ON position):

Green wire: 1.50 V
Black/Yellow wire: 12.0 V
Red wire: 12.8 V
White wire: 0 V

There is continuity between ECU pin 41 and the white wire at the alternator connector (it beeps).

ECU pin 41: 4.9 V

Thick cable (with red cap) at the alternator: 12.8 V

SRS connector (passenger side) was unplugged and cleaned with contact spray.

My instrument cluster doesn't have an "ALT" light; unfortunately, it's not equipped with one.

I'm not exactly an expert on automotive electronics, but perhaps the data I've gathered will help us.

Maybe the car's sound system caused the damage—I have no idea.

 

[Vladimir]

Hello again. Here are the readings from today:

Battery: 13.1 V

Alternator connector (ignition in ON position):

Green wire: 1.50 V
Black/Yellow wire: 12.0 V
Red wire: 12.8 V
White wire: 0 V

There is continuity between ECU pin 41 and the white wire at the alternator connector (it beeps).

ECU pin 41: 4.9 V

Thick cable (with red cap) at the alternator: 12.8 V

SRS connector (passenger side) was unplugged and cleaned with contact spray.

My instrument cluster doesn't have an "ALT" light; unfortunately, it's not equipped with one.

I'm not exactly an expert on automotive electronics, but perhaps the data I've gathered will help us.

Maybe the car's sound system caused the damage—I have no idea.

Just to make sure. You are getting 4.9v at the ECU PIN 41/ Green wire, but you are only getting 1.5v on the same Green wire on the alternator connector? That would indicate excessive resistance such as corrosion etc..

Also the white wire should be ground from the ECU, it would read 0v with a multimeter, which is fine, but it's shouldn't be continuous with pin 41. Maybe you got a problem at the alternator connector or the wiring harness both wire are shorting against each other.

Blk and yellow 12v is good

Red 12v is good

13.1 at the battery is kinda low especially without major load, but borderline pass.


Do a resistance test on that green wire from pin 41 all the way to ALT connector, if there is excessive resistance that would be the problem, you are loosing 3.5volts somewhere from ECU to ALT on that wire. Also that green wire goes from ECU through connector A-32 before it makes it to the alternator. Might be an issue there.

Double check

 

[Taskin]

Just to make sure. You are getting 4.9v at the ECU PIN 41/ Green wire, but you are only getting 1.5v on the same Green wire on the alternator connector? That would indicate excessive resistance such as corrosion etc..

Also the white wire should be ground from the ECU, it would read 0v with a multimeter, which is fine, but it's shouldn't be continuous with pin 41. Maybe you got a problem at the alternator connector or the wiring harness both wire are shorting against each other.

Blk and yellow 12v is good

Red 12v is good

13.1 at the battery is kinda low especially without major load, but borderline pass.


Do a resistance test on that green wire from pin 41 all the way to ALT connector, if there is excessive resistance that would be the problem, you are loosing 3.5volts somewhere from ECU to ALT on that wire. Also that green wire goes from ECU through connector A-32 before it makes it to the alternator. Might be an issue there.

Double check

Hi Vladimir,

According to Google and AI, the one in the picture—on my control unit—is supposed to be the "41" connector.

Where is connector A-32 located?

I’ll double-check everything once I have a new multimeter. My multimeter leads burned out because I left them on the exhaust manifold when I started the engine

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[Vladimir]

Hi Vladimir,

According to Google and AI, the one in the picture—on my control unit—is supposed to be the "41" connector.

Where is connector A-32 located?

I’ll double-check everything once I have a new multimeter. My multimeter leads burned out because I left them on the exhaust manifold when I started the engine

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Green wire should be PIN 41. Voltage coming out from the ECU should be the same as the voltage going in on that same green wire going into the Alternator. You should not be loosing 3.5 volts there. The circuit from the ECU to ALT on that green and white wire goes through another big connector A-32 not sure where it's located on a 2g, I have a 1g DSM. If there is damage or corrosion in A-32, that could also be a problem.

But for now, it's no point of looking for electrical issues without a working multimeter.

Once you get a new meter, just check the green wire from pin 41 to the green wire on PIN 4 of the alternator, resistance needs to be as close as possible to O ohms. According to your previous testing you lost 3.5v on that wire, that would make sense why p1500 code is stored in your ECU.

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[Taskin]

Green wire should be PIN 41. Voltage coming out from the ECU should be the same as the voltage going in on that same green wire going into the Alternator. You should not be loosing 3.5 volts there. The circuit from the ECU to ALT on that green and white wire goes through another big connector A-32 not sure where it's located on a 2g, I have a 1g DSM. If there is damage or corrosion in A-32, that could also be a problem.

But for now, it's no point of looking for electrical issues without a working multimeter.

Once you get a new meter, just check the green wire from pin 41 to the green wire on PIN 4 of the alternator, resistance needs to be as close as possible to O ohms. According to your previous testing you lost 3.5v on that wire, that would make sense why p1500 code is stored in your ECU.

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I did some welding work on the strut tower and the inner wheel arch area on both sides six months ago. I wonder if a stray spark damaged a cable back then... hmm.

 

[Vladimir]

Could be. Also might be the reason SRS is ON, if you damaged the wiring to impact sensors or something in that harness. Check and read the manual, it will show you what's routed through a-32. That harness probably is very close to fender well and strut tower

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[Taskin]

Could be. Also might be the reason SRS is ON, if you damaged the wiring to impact sensors or something in that harness. Check and read the manual, it will show you what's routed through a-32. That harness probably is very close to fender well and strut tower

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Oh, cool, thank you, Vladimir.

 

[luv2rallye]

I did some welding work on the strut tower and the inner wheel arch area on both sides six months ago. I wonder if a stray spark damaged a cable back then... hmm.

Arc welding? You must always disconnect battery and unplug ECU before any arc welding or devices/wiring can get zapped from voltage spikes.

 

[Taskin]

Arc welding? You must always disconnect battery and unplug ECU before any arc welding or devices/wiring can get zapped from voltage spikes.

Yes, arc welding. The battery was disconnected, but unfortunately I didn't think about the control unit.

 

[luv2rallye]

Alternator connector (ignition in ON position):

Green wire: 1.50 V
Black/Yellow wire: 12.0 V
Red wire: 12.8 V
White wire: 0 V

Without engine running, the ECU floats (disconnects) the white wire so it then will read 0v when you put your multi-meter lead on it. Normally with the engine running you will have voltage there. When the engine is running and a heavy load occurs, the factory alt is designed (but many aftermarket alts don't support) so that should the ECU force this wire to a hard (ie. not floating) 0v ground, the alt won't put out more than 12.5v maximum. This is used during hard acceleration to transfer more power to the wheels at that time rather than to use it to also run the alt. So it becomes a duty cycle signal so the ECU can control alt output to what it wants.
However you should measure the white wire voltage while idling to at least make sure it is not 0v (or your alt may not charge the battery).

SRS connector (passenger side) was unplugged and cleaned with contact spray.

So did the SRS light go off?

My instrument cluster doesn't have an "ALT" light; unfortunately, it's not equipped with one.

Are you sure? Every car in the world has a light to indicate the alt is not working. It might be called something different or it is not working. It should go on when you first turn the key to ON without engine running. As I said, the generator relay is supposed to be a backup should that happen.

Maybe the car's sound system caused the damage—I have no idea.

Unlikely. It however, could easily be due to your welding.

 

[luv2rallye]

Yes, arc welding. The battery was disconnected, but unfortunately I didn't think about the control unit.

To be fair, in the REAL world mechanics/repair people can't be expected to know where every ECU is on every model of every car on the planet, let alone take days trying to figure out how to get to them and unplug them all correctly. It just ain't going to happen. So disconnecting the battery and having multiple welding grounding cables to the frame and body is really all you can do. All ECU's are normally protected against some voltage spikes but there is a limit.

 

[Taskin]

Without engine running, the ECU floats (disconnects) the white wire so it then will read 0v when you put your multi-meter lead on it. Normally with the engine running you will have voltage there. When the engine is running and a heavy load occurs, the factory alt is designed (but many aftermarket alts don't support) so that should the ECU force this wire to a hard (ie. not floating) 0v ground, the alt won't put out more than 12.5v maximum. This is used during hard acceleration to transfer more power to the wheels at that time rather than to use it to also run the alt. So it becomes a duty cycle signal so the ECU can control alt output to what it wants.
However you should measure the white wire voltage while idling to at least make sure it is not 0v (or your alt may not charge the battery).

So did the SRS light go off?

Are you sure? Every car in the world has a light to indicate the alt is not working. It might be called something different or it is not working. It should go on when you first turn the key to ON without engine running. As I said, the generator relay is supposed to be a backup should that happen.

Unlikely. It however, could easily be due to your welding.

Yes, the SRS light is still on.

The Picture shows which lights come on.

When I start the engine, the SRS light stays on.

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[Taskin]

To be fair, in the REAL world mechanics/repair people can't be expected to know where every ECU is on every model of every car on the planet, let alone take days trying to figure out how to get to them and unplug them all correctly. It just ain't going to happen. So disconnecting the battery and having multiple welding grounding cables to the frame and body is really all you can do. All ECU's are normally protected against some voltage spikes but there is a limit.

Unfortunately, I didn't think that far ahead. You learn from your mistakes.

 

[Taskin]

Without engine running, the ECU floats (disconnects) the white wire so it then will read 0v when you put your multi-meter lead on it. Normally with the engine running you will have voltage there. When the engine is running and a heavy load occurs, the factory alt is designed (but many aftermarket alts don't support) so that should the ECU force this wire to a hard (ie. not floating) 0v ground, the alt won't put out more than 12.5v maximum. This is used during hard acceleration to transfer more power to the wheels at that time rather than to use it to also run the alt. So it becomes a duty cycle signal so the ECU can control alt output to what it wants.
However you should measure the white wire voltage while idling to at least make sure it is not 0v (or your alt may not charge the battery).

So did the SRS light go off?

Are you sure? Every car in the world has a light to indicate the alt is not working. It might be called something different or it is not working. It should go on when you first turn the key to ON without engine running. As I said, the generator relay is supposed to be a backup should that happen.

Unlikely. It however, could easily be due to your welding.

Yes, I will do the measurement at idle as soon as I have a new measuring device, thank you.

 

[luv2rallye]

That battery icon light below the Brake light is your Charge (aka alt) light.

 

[Taskin]

That battery icon light below the Brake light is your Charge (aka alt) light.

Ah, okay—learned something new. Thanks.

 

[Taskin]

That battery icon light below the Brake light is your Charge (aka alt) light.

Just an idea: what if I ran a bypass cable between connector 41 (control unit) and the alternator connector—just routing it externally and somehow splicing it into the connectors? Would that make sense? I wonder if the error might go away... hmmm.

 

[Taskin]

Could be. Also might be the reason SRS is ON, if you damaged the wiring to impact sensors or something in that harness. Check and read the manual, it will show you what's routed through a-32. That harness probably is very close to fender well and strut tower

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