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Treystoys 04-01-2021 08:31 PM

Communications link error, service vehicle and brake warning
How’s it going everyone. I just picked up a high mileage 04 Ion 2 sedan. The car is in pretty good shape cosmetically, a little funky inside, a bit clunky suspension wise, but actually runs and shifts great and has cold AC. It’s a car for my teen to go back and forth to school, practice...

So, as my thread title says, I have the service vehicle and brake warning lamps lit, and I get a communications link error with my scanner and I have attempted to use 3 different scan tools, all giving me the same error message.

So first, the brake light...the reservoir is full of brake fluid, the connector is plugged into the sensor (have not pulled the sensor yet to look at it or checked for float operation if there is one?) and the grounding strap on the e brake handle has continuity and looses it as per its design.

I found the fuse blown for the lighter and got very excited thinking the scanners would link, but no dice, fuse still intact and none of the readers I’ve used will link.

The service vehicle light? I don’t know, is it tied to the brake light and link error or one or the other? I’m kind of thinking it’s tied to the brake light issue, but am still brainstorming it.

The car has another issue dealing with the door locks. The issue being sporadic working but most times not, and sometimes all or some will unlock when I shut the car off and open the drivers door.

It would be easy to call all of it a bcm issue, but I don’t know. I have a reasonable skill set with regards to automotive repair, part of which involves researching before hand, which landed me here. This being a car I am keeping, I figured I’d join up here and get sone help with the researching.

Thanks in advance! and my name is Trey

fdryer 04-02-2021 03:09 PM

Re: Communications link error, service vehicle and brake warning
Search within this forum for wiring diagrams, pinouts for the obd connector. Pin-16 is fused for 12v. Pins 4 and 5 are ground. If pin-16 doesn't have 12v, a fuse is blown. Your owner's manual should have info on fuses or check fuses manually. Check to be sure the obd connector wiring is intact. There are either two or three fuse panels, main engine and one or two inside the car by the console or footwell area. Google for OBD II pinouts - the main serial comm for reader connection is pin-2. Check all fuses as the bcm has its own set of fuses. I don't know what fuse powers the obd connector.

The brake light remaining on doesn't turn on the check engine light directly as all error codes generated come from the bcm via the obd connector connected to a reader. The brake light is either the low brake fluid switch on the brake master cylinder or the parking brake switch. Both are normally open, ungrounded when brake fluid is above the low level mark and brake lever released. When below low level, the brake master cylinder switch closes, connects to ground to send a ground signal to the bcm. The brake lever pulled allows the park brake switch to close, connecting to ground to send a signal to the bcm. The bcm turns on the red brake light indicator for either low fluid or pulled brake lever. One way to test for a damaged brake fluid level (rare) or park brake switch (likely) is to disconnect each one with ignition on. Disconnecting wiring physically disconnects a ground connection and should turn off the brake light.

Check overall wiring harnesses for dry rot, chafed insulation, corroded connections. The bcm runs everything unrelated to the ecm running the EFI system except airbags and abs/tc. Those have their own modules. Error codes turning on the check engine light come from the bcm with all modules sending their messages to the bcm for direct output to a reader. The engine light only outputs P type codes. The wrench light outputs B, C, and and U codes. Generic readers only decode P type errors. Autozone can decode abs errors.

Either the obd connector is damaged from meddling or power is missing on pin-16.

Treystoys 04-03-2021 07:08 AM

Re: Communications link error, service vehicle and brake warning
Thanks a bunch for responding!

So I had already checked the fuse box in the forward center console and the one in the engine compartment. By checking I mean I used my power probe to make sure all fuses had power and continuity. All the mini fuses were fine. One of the first things I did, even before I bought the car was to pull the obd plug out and apart, pin by pin to check for physical damage, but I did not have a pin out on me when I did it, so I’ll pull up a diagram and test for voltage there, maybe it’s a bad wire. Or like you said, not necessarily damage, but now I’m wondering if it would have a wire in the wrong spot.

The brake light is weird, I had both the reservoir plug and the ebrake plug off, but I don’t remember if I did them both at once. I had pulled the console out prior to clean it and check on the switch, again I’ll double check, but that was working properly. I’m leaning towards the reservoir. It is full, but the fluid is dirty, so I am going to empty it and physically check the float, maybe it’s stuck to the bottom. At any rate it will allow me to introduce some fresh fluid to the system without a full flush. If nothing I’ll look for the short.

So to be clear, there is no check engine light. The check engine light comes on on start up and then goes off like normal. The light that is on is the warning that says “service vehicle” I can clear it with the trip tick button but it comes back on anytime the ignition is cycled.

The last code reader I used is brand new. It’s mid tier but does obd/can, abs, srs, freeze frame and live data. I just bought that one as an excuse to replace my 20 year old pocket scanner, which of course I tried on the car, as well as our scanner that we keep around the shop. Lol my later train of thought on that was from a search on either this or another Saturn forum, someone mentioned the Ion using canbus communication and I know my pocket scanner does not use that, and I wasn’t 100% that the Innova we had at work was new enough for canbus either, so I made that my excuse to buy the new reader, again with the hopes that it was just the reader having the issue, but no avail, I got the same link error on all of them.

Again, thanks for responding, I’ll update as I progress!


fdryer 04-03-2021 12:37 PM

Re: Communications link error, service vehicle and brake warning
An '05 owner's manual states;
"Service Vehicle Message - If the SERVICE VEHICLE message is displayed, a non-emission related problem has occurred which requires the vehicle be taken in for service."

If I can presume all Ions use the same error messaging program then the inability to connect a reader to the obd port may be reason for the service vehicle message. Most Saturns have a wrench indicator for the same description. Non emissions related errors, B, C and U type error codes cannot be decoded by generic readers as these codes are manufacturer specific and require GMs Tech II scantool, relatively low cost aftermarket reader/scantool capable of decoding GM non emissions related error codes or commercial quality reader/scantool like Snap-On used by repair shops. I bought VCX NANO (<$100) as a GM scantool clone. There may be others at low cost, dedicated to each manufacturer. VCX offers other scantools for other vehicle manufacturers. I needed this to verify a wrench light error code pointing to one of the xmission solenoids, P1811, that doesn't appear on a generic reader. I used it to program spare remotes too. Yes, this is a P type code but never appeared in my reader prior to acquiring a VCX NANO, likely due to the wrench indicator turning on and not the engine indicator.

For now, it seems a priority to determine obd connections and/or power before connecting a reader is possible.

Treystoys 04-05-2021 07:23 PM

Re: Communications link error, service vehicle and brake warning
Just a quick update. The obd plug does have battery voltage at 16, and I have confirmed ground at 4 and 5. Still digging.

Treystoys 04-05-2021 08:43 PM

Re: Communications link error, service vehicle and brake warning
Positively noted update. New scan tool is connecting now. Apparently in my now known reckless checking of the obd plug prior to buying the car (back when I was attempting to scan it with non can based scanners) I carefully (so I thought) pulled each pin from the connector, inspected it, and reinserted it. Well I failed to reinsert pin 6 ďcan highĒ fully and that caused my link error. Rechecking my old scanners, they still do not link, but the new Innova I just bought does, so thereís my plus!

The car had no DTCs present, but then I pulled the SRS codes and came up with b1001, u1000, u1016, and u1096. Which erased with the scanner, and did not pop up on an immediate rescan. Again, I have no check engine light, no airbag light, and everything functions and runs as it should. I even got the door locks working again with an auto unlock/lock feature reset. Researching those codes all points to faults that would lead to what Iíd think make their respective indicator lights come on and stay, and again, they all function on start up then go off as if normally functioning, minus the brake light. I still havenít drained the m/c reservoir yet to test the float and sensor, so thereís that.

Thanks again!

Treystoys 04-10-2021 03:01 PM

Re: Communications link error, service vehicle and brake warning
So I can confirm that the parking brake switch circuit works. A driving test with the parking brake handle slightly elevated makes the warning charm go off, fully releasing it makes it go away, but the light stays on. I pulled the fluid switch again and ohm tested it and get 17-22 normally then applying a magnet to the top makes it go to 2 ohms, or these may be mili ohms I forget. These reed switches have resisters in them, so it is possibly out of spec?

I’d grab a new one and try it just because, but I cannot find a switch anywhere, and most searches turn up out of stock no back order, or discontinued.

I guess the local pull a part would be an option, but I’d love to get my hands on a new one, or possibly a known resistance for an open circuit so I can possibly put a resister in-line of the two leads. Jumping them out with a paper clip does not seam to work. I keep thinking back to my subaru days, when aftermarket seats or steering wheels were installed, we would put a resister into the seat and steering wheel air bag connectors to turn those lights off and keep the srs happy.

Any thoughts would be great!



fdryer 04-10-2021 08:09 PM

Re: Communications link error, service vehicle and brake warning
I'm not familiar with Ion master cylinder low brake fluid switches but other similar low brake fluid switches do not use resistors. A review of my service manual for my L300 shows a simple on/off switch in the wiring drawing. When brake fluid drops below the low level mark, the normally open switch closes, connecting ground to the bcm. The bcm interprets this as low fluid level and turns on the red brake light. Filling the mc with fluid with the float rising opens the switch removing the ground connection. The bcm not sensing a ground turns off the brake light. I presume this circuit applies to virtually every master cylinder low level switch circuit. Please correct me if I'm wrong.

If I'm not mistaken, the switch should measure zero resistance/open when float is high, closed/short when float is down. Disconnecting the wire to the mc should result in the brake light off. This presumes the parking brake switch is also closed/parking lever released in down position or wire to this switch also disconnected.

Treystoys 04-11-2021 06:00 PM

Re: Communications link error, service vehicle and brake warning
If we are to believe 95% of whatís out there online then that would work, but not the case with this system, maybe thatís why parts have been discontinued for it, I donít know. Unplugging it here turns the light on. I think itís more of a sensor than just a switch in that voltage will vary past a certain point of the floats position relative to the magnet in the float. Believe me, this single little circuit threw me for a loop too.

I do have good news though, I spent a few hours at Pull-a-part this morning, and along with a few other items I grabbed 2 upper m/c reservoirs with the sensors. The first sensor I plugged in fixed the issue. The brake light and service vehicle message are gone. I didnít even have to swap out the old reservoir. I didnít put the voltage meter on it again or ohm it out, I was just excited to have fixed it. Aside from a small rear main seal leak and a little strut bearing noise, the car is good to go.

On a side note, that was my first trip ever to pull a part. Iíve been a mechanic most of my adult life, and donít know why I had never gone. I bet I got $300 worth of good used parts for $60 and that was being very picky as they had probably 20 Ions. Itís a shame, I just spent $290 on a set of tires for this thing, and they had an 07 ion with the 5 spoke 16s, with brand new tires, dot date 2020, they still had the rubber nipples on the surface. $160 for the set! Oh well.

Thanks again for following along! I guess we learned something here lol


fdryer 04-12-2021 12:52 AM

Re: Communications link error, service vehicle and brake warning
You may be less than a handful of members here with a faulty low brake fluid switch. As you found, junk yards have perfectly working spare parts. Saturn wasn't discontinued due to odd circuitry.

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