Cause Of Brake System Warning Light Remaining On After Disengaging Parking Brake?

[The Swamp Fox]

Hello all! I am new to the forums here, but my wife and I have owned an '05 Chevy Aveo LS hatchback (1.6L, MT) since 2011. I'm currently troubleshooting an issue that has been present for some time now — the red brake system warning light on the dash is remaining on after the emergency/parking brake lever has been released.

This light has been on now for a little over a year, and I'm just now getting the time to troubleshoot it. A bit of background for sake of context might be helpful — the car has only 65,000 miles on it to date, and has had no significant issues since we've owned it. I performed a full four-wheel brake service 3.5 years (6,000 miles) ago, including the following:

• Replaced the front brake calipers, rotors, pads, and hoses
• Inspected, cleaned, and adjusted the rear drum brakes and parking brake
• Bled the entire brake system per repair manual procedure

I'm fairly convinced that this is somehow related to a faulty sensor or switch rather than indicating an actual fault in the braking system, in light of the brake system service performed only 6,000 miles ago and the below data points:

• The rear brake lights are functioning properly
• The car does not pull to one side or the other when braking
• The parking brake is used on a regular basis and is fully functional. It engages fully and is capable of holding the car still even on an incline, releases fully and does not drag, and has the expected impact on the DRL
• The brake fluid reservoir is full, ruling out low brake fluid as the culprit
• I've examined each wheel closely for signs of slow leaks from brake bleeders, lines, calipers, or wheel cylinders and have found none
• The brake system warning light is on steady as opposed to flashing intermittently
• There are no Check Engine Lights or ABS System warning lights showing on the dash
• I have used a ScanGauge E to scan for CEL's and fault codes, and it comes up empty

With all of the above in mind, I'm proceeding with the hypothesis that the warning light is being thrown by a faulty switch or sensor of some sort. I'm no rookie under the hood, but tracking down electrical gremlins has never been a strong suit.

I searched the forums here prior to posting but found only two related threads, one of which the cause turned out to be low brake fluid, while the other contained no listed resolution. After some additional searching online, I came across an article from Your Mechanic listing six possible causes. Hoping for an easy solution, I performed the following tests to no avail:

1. Jiggled parking brake lever aggressively in the down position
2. Used significant downward pressure to ensure parking brake lever was fully released
3. Verified brake fluid reservoir fluid level

Pages 11–20 of the "Hydraulic Brakes" section of the Service Manual (attached) contain a Brake Warning System troubleshooting workflow. In the course of following it, I disconnected the wiring harness connector to the Brake Fluid Pressure Sensor located on the Brake Fluid Reservoir, and found that doing so turned off the warning light on the dash for about two cycles of the emergency brake, after which it resets.

This leads me to believe the Brake Fluid Pressure Sensor could be faulty. For those of you curious what this part looks like, it's available at Rock Auto for $18.88 + shipping, and Wikipedia has a brief write-up on how these sensors usually work.

Rather than work off of a hunch and risk simply throwing money and parts at the problem, I was hoping to find a way to definitively prove the switch was faulty. Additional research online turned up this YouTube video comment regarding the possibility of a float tied to said pressure sensor possibly getting stuck inside the reservoir. Unfortunately, no float is visible through the reservoir's cap, and I tried tapping the side of the reservoir with a screwdriver to no avail.

I then came across another YouTube video demonstrating how to test the switch via the continuity setting on a multimeter. I performed this test myself and found no continuity between the two pins on the sensor's electrical connector, which would appear to indicate the sensor is not my issue.

Before I start off on various wild electrical goose chases, is there anything simple I've overlooked to date? Anyone else have experience with this particular issue or a recommended way to test the brake fluid pressure sensor for proper operation?

[The Swamp Fox]

Well, I have somewhat of a new development. The Parking Brake Light on the dash will now consistently go out after starting the car and releasing the parking brake, but resets in about 3–5 seconds and then stays on steadily no matter how many times the parking brake is set or released. Turning the car off and then back on will result in this same cycle all over again.

I've tested this without touching the actual floorboard-mounted brake pedal, and nothing changes. This leads me to believe that the light is not coming on to indicate a pressure differential in the braking system, since there would be zero pressure applied from the time the key is turned to the time that the light first presents.

Given this and the fact that the light is now going out when the parking brake is first released, I am leaning even more strongly toward a faulty brake fluid switch being the problem. Would love to hear someone else's thoughts prior to my simply throwing parts at my best guess, however. Any takers?

[The Swamp Fox]

Anybody? Bueller?

[avguy]

This forum isn't very active these days, so I don't visit much anymore. Anyway, I suggest taking a look at the parking brake switch, connector, and nearby wiring for issues. The console hood and parking brake assembly need to be removed in order to access to the switch/connector.

[MetroMPG]

Any update, Swamp Fox? Did you solve it?

[kcROB]

This post deleted by the author.

[kcROB]

This post deleted by the author.

[The Swamp Fox]

Any update, Swamp Fox? Did you solve it?

I have been waiting to update this thread with my final resolution, but figured an update was due since I recently discovered that the plot of my sorry saga has somewhat nefariously thickened.

For sake of reference, here are the troubleshooting steps I had attempted as of my original post, guided by the troubleshooting flow chart in the service manual:

1. Checked for low brake fluid in the reservoir, but found that it was full.
2. Inspected brakes at all four wheels and found no evidence of leaks or worn pads (replaced 6,000 miles ago).
3. Tested the parking brake and verified that it can hold the car still when on an incline, that the rear wheels can spin freely when the brake is disengaged, and that the parking brake has the expected impact on the DRL when set and released.
4. Jiggled the parking brake handle and applied significant downward force when releasing it to see if this had any impact on the BWL, which it did not.
5. Checked the operation of the rear brake light bulbs and found that they were working as expected.
6. Used a ScanGauge E OBDII reader to scan for Diagnostic Trouble Codes, and found none.
7. Disconnected the battery terminals for several hours to reset the Brake Warning Light, only to find that it promptly came back.
8. Tested the brake fluid level switch terminals for continuity with a multimeter and found none, indicating the switch is open and is therefore performing as expected.
9. Disconnected the brake fluid level switch to isolate it from the circuit and see if it turned off the BWL, which it did not.

At this point I figured I had eliminated most, if not all, of the common causes and easy troubleshooting steps without getting any closer to a resolution. The only thing I hadn't checked was the parking brake switch itself, so I then performed the below two steps:

1. Inspected the parking brake switch and wiring under the center console for shorts or loose connections, and found none.
2. Disconnected the parking brake switch to isolate it from the circuit and see if it turned off the Brake Warning Light, which it did not.

False Hope
At this point I was scratching my head pretty good, so I went back over some of my previous troubleshooting steps and performed them a second time to rule out any false negatives.

One of these steps was the rear brake light bulb check. When I had initially tested the rear brake light bulbs, I was working alone and therefore evaluated them via the reflection off of the back wall of the garage, as seen in each side view mirror. I could see the CHMSL bulb was working via the visible glow around the edges of the bulb housing in the hatchback area.

For the re-test, I used a 2x4 wedged against the seat track to depress the brake pedal so I could step back and actually view the rear of the car. When I did so I began berating myself, as I immediately noted that the DR upper brake light bulb was out!

This did not show up in my previous test of the bulbs since there are actually TWO (one upper, one lower) brake light bulbs on each side, and the one bulb that was working threw a visible brake light reflection on the driver side rear. I was unaware that there was more than a single bulb on each side.

Thinking that I had (finally) hit upon my problem, I ordered a replacement bulb from Rock Auto. But after installing it, I found to my frustration that the BWL was still illuminated.

Doubling Down On The Brake Fluid Level Switch
At this point, I was just about certain that the problem was in some way related to the brake fluid level switch, which I had read is a common culprit for triggering the BWL. I ended up performing several additional related tests focused on it as the issue:

1. I pulled a different switch out of another Aveo at my local Pick-a-Part and installed it, with no change in results.
2. I re-tested the the brake fluid level switch terminals for continuity and again found none, indicating the switch is open and should not be the cause of the BWL.
3. I tested the harness-side brake fluid level switch connector for resistance with the key in the "On" position, and found about 84 Ohms of resistance. I then plugged the brake fluid level switch back in and back-probed the harness side connector and obtained a reading of "Open Loop", indicating the switch is staying open even once plugged in. This definitively rules out the switch as the cause.

Ruling Out Anti-Lock Brakes
In the absence of Anti-Lock Brakes (ABS), the troubleshooting workflow in the Service Manual more or less limits the possible causes of the Brake Warning Light coming on to a brake malfunction, low brake fluid, or a malfunction in the brake fluid level / parking brake switch circuits, the Lamp Driver Module (LDM) in the instrument cluster, or the Electronic Brake Control Module (EBCM).

I've driven both cars that were equipped with ABS and those that were not, and am familiar with the difference in pedal feel when the ABS kicks in. Since the Aveo has been my daily driver through many Michigan winters and I had never felt any ABS operation, I was pretty positive that it wasn't so equipped.

However, in the interest of due diligence I consulted the Owner's Manual to find where the ABS indicator light would be located. I found that it should be in the upper right of the Secondary Information Center (SIC) — a fancy term for the clock unit — if the car is so equipped. I then cycled the key a few times to enable the various indicator bulb checks, and confirmed that no ABS light was present.

Testing the Electronic Brake Control Module
Since my testing to this point had ruled out everything but the LDM and EBCM, I began focusing my troubleshooting on these two items per the troubleshooting workflow in the Service Manual:

1. Tested battery voltage to rule out low supply voltage to the EBCM resulting in a malfunction, and obtained 12.13V indicating this is not an issue.
2. Visually inspected the condition and amp-rating of all fuses in the passenger compartment fuse panel and found none that were blown, missing, or misplaced.
3. Visually inspected the condition and amp-rating of all fuses in the under-hood fuse box and found none that were blown, missing, or misplaced.
4. Swapped all brake or EBCM-related fuses with known good fuses of the same amperage and cycled the key to see whether the Brake Warning Light was out, but it remained on.

An Unexpected Discovery
During all of my fuse inspections, I though it was odd that all of the ABS-related fuses and relays were present, although the fuses required to power other optional accessories my Aveo is not equipped with — such as fog lights and power windows — were not.

And while working to disconnect the EBCM harness connector (which required removal of the windshield wiper motor housing and coolant overflow tank) for some pin-out testing, I noticed that the brake lines from the master cylinder were routed to a boxy object screwed to the EBCM.

I was also missing the dual proportioning valves at the master cylinder that should have been there to control front/rear braking forces. Some online digging in the Rock Auto parts catalog revealed that sure enough, the boxy object attached to the EBCM under the coolant overflow tank was in fact an ABS Brake Modulator!

I pulled the build sheet from Chevy and it lists ABS as an included option as well. This was a huge surprise, as I've never felt the ABS system kick in throughout the nine Michigan winters I've driven this car daily, and I've never seen the 3-second ABS system bulb check that the Owner's Manual calls for.

Evidence Of Tampering
Armed with this new information, I consulted the troubleshooting steps in the Service Manual workflow that were ABS-system specific, which I had ignored up until this point. It stated that failure to light the ABS System indicator on the clock could be caused by either a bad EBCM or bad Lamp Driver Module (LDM).

Per the Service Manual, the default operating condition of the Lamp Driver Module is to run the ABS System indicator and Brake Warning Light always on, unless a cancelling signal is received from the EBCM. Therefore, unplugging the EBCM wiring harness should indicate that the problem lies in either the EBCM (ABS light comes on) or the LDM (light remains out).

I unplugged the EBCM harness connector to isolate the circuit, but the Brake Warning Light remained on upon cycling the key, while the ABS light did not come on at all.

This test seemed to rule out the EBCM as the culprit and instead point to the LDM. However, I thought it strange that the Brake Warning Light was working fine while the ABS light was not, since they're both controlled by the LDM. So I decided to check for a burned out ABS System bulb in the Secondary Information Center (SIC) near the clock unit.

Access wasn't difficult, but I found it interesting that one of the upper trim panel retaining screws differed from the other and looked like a standard machine screw. And while removing the back from the clock face, I found that one of the locking tabs had been broken.

After getting the two halves of the clock apart, I found that the ABS light bulb is completely missing! It appears to have been there at one time as indicated by some discoloration where the base would have been, but it is currently gone. No wonder the light isn't lit!

I believe the differing screw, broken locking tab, and missing bulb are likely the result of someone who decided to pull the ABS light bulb in order to hide the idiot light for resale purposes. As mentioned, I've never felt the ABS system kick in since I purchased the car in 2011. This likely means that there has been an underlying fault in the ABS system for over nine years that has prevented the EBCM from activating it.

More than likely, another fault in the EBCM system occurred a year or so ago when the Brake Warning Light first illuminated. Per the Service Manual, the Brake Warning Light will illuminate on ABS systems when certain specific ABS faults are identified which are considered serious enough to impact overall braking system performance, like two bad wheel speed sensors on the same axle.

Next Steps
Now that I know the car has an ABS system, I took it out on a nearby gravel road and locked up the wheels a few times and confirmed that the ABS system is currently non-functional. Per the service manual, this could be due to any number of ABS-specific error codes.

My plan of attack is to obtain an OBDII scanner capable of reading and resetting ABS fault codes so I can learn exactly what ABS error the EBCM is reporting, and to obtain a replacement bulb for the ABS System indicator light on the SIC.

I haven't had any luck at all obtaining any information on bulb replacement size, type, or process. Are these LED bulbs in fact replaceable, or does the entire clock/SIC unit have to be replaced?

[The Swamp Fox]

One last update for sake of future reference by any poor souls who find themselves in a similar predicament.

I first purchased a replacement dash clock / secondary information center to replace my unit with the missing ABS light. This was a stupidly difficult process, as three different units from eBay all proved defective in one way or another. If you go this route, be sure to buy only those with a money back guarantee and free return shipping, as I did. I ended up finding a working unit from my local pick-a-part.

After installing, I verified that my ABS warning light was in fact on. This meant that there should be an ABS system-related code stored in the ABS module. I ended up purchasing the OTC Tools 3208 OBD-II scanner which doubles as an ABS code reader for certain models, including the Aveo.

The scanner was capable of reading ABS module codes that my normal OBD-II scanners (ScanGaugeE & Kiwi 3) could not. The initial scan came back with 8(!!!) ABS-related codes:

1. C1200 — Left Front Wheel Speed Sensor Circuit Open or Shorted
2. C1201 — Left Front Wheel Speed Circuit Range / Performance
3. C1202 — Left Front Wheel Speed Sensor Input Signal Equals Zero
4. C1203 — Right Front Wheel Speed Sensor Circuit Open or Shorted
5. C1206 — Left Rear Wheel Speed Sensor Circuit Open or Shorted
6. C1207 — Left Rear Wheel Speed Sensor Circuit Range Performance
7. C1208 — Left Rear Wheel Speed Sensor Input Signal Equals Zero
8. C1209 — Right Rear Wheel Speed Sensor Circuit Open or Shorted

I cleared all of these codes, ran the car for a bit, then re-scanned and found that only C1200, C1203, C1206, and C1209 had reset. All of these were related to the ABS wheel speed sensors, which pointed me in the right direction in the troubleshooting workflow.

I checked all of the ABS wheel speed sensor wiring for obvious damage or shorts, and found none. I then disconnected the ABS sensors at each wheel and tested their resistance with my multi-meter. The service manual says they should spec out between 800–1,600 Ohms. I pulled the below readings:

• DF — Infinite resistance (open loop)
• PF — 12.8 million Ohms
• DR — 300,000 Ohms
• PR — 2,450 Ohms

All of these were obviously out of spec, so I ended up ordering four replacements for around $50 total from Rock Auto. The replacement isn't complicated by design, but my old sensors were solidly stuck in place. I had to end up burning them out with a propane torch and picking out the remnants with a pick. Took the better part of an afternoon.

After replacement was completed and I had re-cleared the ABS codes once more, the codes have yet to return. It appears my problem is solved. Finally!

[kcROB]

Very impressive amount of research, diagnosis n execution protocol. I didn't understand some of it, but I congratulate you for making it available to Aveo owners.