CEL - P1518 Starter switch circuit low input

[jib]

The subject says it all. I've thrown

 

CEL P1518 Starter switch circuit low input

 

on my 02 Legacy GT, 5 speed Wagon, but don't quite understand what this CEL is trying to tell me. Can anyone provide some help on trying to figure this one out.

 

The starter may be starting to sound just a tad different; I'm not sure, it's hard to tell with the change in outside temperature, and the car has 99.3K miles.

 

Thanks in advance,

 

Jack

[ferret]

The ECM is monitoring the Starter +12v. If the car is starting and running correctly, this is a false error. But may indicates a poor or broken wire from the starter +12v solenoid to the ECM.

 

I would check the connections at the starter solenoid ( the smaller push on terminal of the solenoid )

 

You did say the starter was sounding odd. This could also be caused by a 'sticky' solenoid. If the engine starts, and the solenoid remains engaged for more than 10 seconds, this will also set a P1518.

 

This should give you a place to start ( no pun intended ). I suspect you will have to replace the started/solenoid.

[jib]

Ferrett,

 

I did just replace a weak battery, so there may have also been a low voltage situation during starting.

 

I'll take a good look at, then dissassemble, clean and re-assemble the starter solenoid wiring and check everything out for corrosion and impedance.

 

I don't believe the starter is in an overrunning situation, it's just not that type of noise.

 

Given the old battery situation, once I've gone through the wiring, I'll reset the code and run it for a while. If that does not do it, I'll pick up a solenoid, then remove and test the old one and yes, I'll disconnect the battery prior to playing with any of the starter electrics. I'm not fond of big sparks in my engine bay.

 

Thanks a lot. I appreciate your help.

 

Jack

[Cougar]

The low voltage warning isn't due to something wrong with the solenoid, which I doubt there is any problem with it since it is pretty new. The warning has to do with the voltage going to the solenoid and that comes from through the ignition switch.

[OB99W]

I agree with Cougar, it's unlikely that the solenoid or the connection at it is the problem (unless the solenoid is drawing very excessive current, in which case a blown fuse would probably result). The ECU monitors the voltage going to the solenoid, and assuming the battery voltage is sufficient, the ignition switch and the neutral safety switch (on a manual; the inhibiter switch on an auto), or connections to them, are the usual culprits when it's low.

[ferret]

I still stand by my original statment. Here's the wording copied and pasted right from the FSM:

( the dash before the speed and rpm is a greater than or equal sign. Didn't paste properly )

 

 

 

 

 

 

Judge NG when the starter signal remains to be ON regard less of both vehicle speed and engine

 

 

 

 

speed become high.

 

 

 

 

 

 

Judge NG when the continuous time of completing all the conditions below becomes more than 10 seconds.

 

 

 

 

Engine speed

 

 

 

 

≥ 1500

Vehicle speed ≥ 30 km/h (19 MPH)

 

 

 

 

Starter “ON” signal Not detected

 

 

 

 

 

 

 

Judge OK and clear NG when the start switch is turned ON to OFF.

[OB99W]

I still stand by my original statment. Here's the wording copied and pasted right from the FSM:[...]

Hmmm, that's interesting -- the factory info I have for Subaru P1518 only mentions the condition where solenoid voltage is low during cranking, not high after start.

 

However, even if the solenoid voltage remains high after start, that wouldn't be due to the solenoid sticking. (The wiring diagrams I have show that the ECU is monitoring the solenoid coil voltage, not that to the starter motor itself.)

[ferret]

Remember when the solenoid closes, thats about 1/2 it's current. The rest is the contacts. Either one is removed and the solenoid drops back enough to dis-engage.

 

From what I read here, After removing the starter 'pick', there is still current sensed.

 

If you have the FSM, you will see how they depict the soleniod. It has 3 connections. 2 are internal.

 

Ground

Pick ( from ignition key )

Contact ( internal ring that also make the contact to turn the starter )

[OB99W]

Remember when the solenoid closes, thats about 1/2 it's current. The rest is the contacts. Either one is removed and the solenoid drops back enough to dis-engage.[...]

I understand that the solenoid has two windings (or a tapped winding, based on the diagram). The external connection is for power to "pull-in". When the internal contacts make, that provides power to "hold-in" (but as you noted, it doesn't really hold if "pull-in" power is removed). However, jib said "I don't believe the starter is in an overrunning situation"; it should overrun if the solenoid sticks.

 

What I find annoying is that different Subaru factory manuals apparently describe the conditions under which the code is set differently, and appear to also have diagnostic procedures that vary. It's not like this is a very complicated circuit. Oh well...

[WAWalker]

Have never seen this code set on an OBD II car.

 

But, on the OBDI, a crank with no start is all it took. Always a false code.

 

JM.02

[Cougar]

I checked the wiring diagram for this and I now see it is wired a little different than a normal solenoid and isn't what I thought it was at first.

 

There is a second coil in the solenoid that is in series with the ignition line and the starter motor windings. The switched line tieing to the battery for the starter is tied in between the connection of the second coil and starter windings. When the key is turned to Start and before the solenoid has time to close, power is applied to the starter windings through the windings of the second coil. This will cause a voltage drop between the coil and the starter windings. When the solenoid closes, the voltage across the second coil will basically be the same on both sides and current will cease to flow through it and all current to the starter will now be through the solenoid contacts. I assume that the load on the battery due to the starter windings, and that will make the battery voltage drop to around 10 volts while cranking, is what the ECU sees as a connection to the starter and makes it happy.

 

I can now see why there could be a problem with the solenoid and cause the error to occur.

[OB99W]

Assuming that the car is really an '02, unless the code was misread, it seems a Subaru with OBD-II has set P1518.

[WAWalker]

Assuming that the car is really an '02, unless the code was misread, it seems a Subaru with OBD-II has set P1518.

 

I was saying I have no input from experiance, due to never seeing this code set on an OBDII car. (Starter switch circuit low input) (I have been around enough to know that OBDI cars do not have P codes)

 

But I do on an OBDI car, and simple crank but no start would set the code on OBDI cars (falsly).

 

The starters really haven't changed.

 

Has what the ECU is monitoring changed?

 

I will step back, as I said, I have no experiance.

[OB99W]

Cougar has described the circuit connections, but I'd like to clarify the operation. "When the key is turned to Start and before the solenoid has had time to close", the "second coil" (pull-in winding) is energized (getting its ground through the starter windings), as is the hold-in winding ; that is, both windings are energized to accomplish pull-in. Since solenoid hold-in requires less force than pull-in, only the hold-in winding needs to remain energized once pull-in has occured, so the pull-in winding is depowered by being shorted out when the contacts make.

 

As to the criteria for setting P1518, apparently Subaru isn't sure. Therefore, whether a bad solenoid can be the cause or not is something I won't take a stand on any longer. If the starter is cranking normally and the code is set, it's likely to just be caused by a bad connection to the ECU's sensing circuit. If the starter is misbehaving, then check the things that can cause that, and when fixed the code will probably go away. How's that?

[WAWalker]

DTC P1518 - STARTER SWITCH CIRCUIT LOW INPUT

DTC DETECTING CONDITION

Two consecutive driving cycles with fault

TROUBLE SYMPTOM

Failure of engine to start

 

[OB99W]

DTC P1518 - STARTER SWITCH CIRCUIT LOW INPUT

DTC DETECTING CONDITION

Two consecutive driving cycles with fault

TROUBLE SYMPTOM

Failure of engine to start

 

Yes, I've got that info also. However, if you read ferret's FSM info, and compare it to jib's circumstances, it doesn't all fit neatly together.

[Cougar]

Thanks for making the operation explination more clear OB99W. I wasn't thinking of the second coil being used as you stated but you (as usual) are correct.

[OB99W]

Thanks for the kind words, Cougar.

[WAWalker]

I guess I don't always clearly type what I mean.

 

If the DTC was set before the battery was replaced. Then I would say.

 

Yes a weak battery could have caused it.

 

I would clear the code and drive on. That is what I have done every time I have seen that code in the past 11 years. There has never been a problem with the starter. It has always been something else that resulted in a no start.

 

Not to say something hasn't changed since the invent of OBDII.

 

If the DTC sets with the new battery in the car, and the cars starts and runs fine. Different story.

[jib]

OK, so it seems like the old battery may have contributed to the issue. I did have two, maybe three, non-starts with the bad battery; once when I first discovered it was dead, and one, possibly two non-starts, as it was being charged. I was late for a meeting and tried to start it before the battery had sufficient charged to fully crank it. FYI - The charger is a old Schauer 10 AMP.

 

I'm going to find the connectors for the solenoid circuitry and open/close the connector a few times to insure there is no corrosion there. I own two Triumphs and old habits die hard. Then I'm just going to pretend that code did not get set and not worry about it, unless it pops up again.

 

Also, it appears that it's finally time for me to log onto the Subie OEM site and download my FSM.

 

Thanks for all of the help guys. I'll report back if the CEL is thrown again.

 

Jack