What Does C1291 Mean?
The ABS/ESC module detected that the brake lamp switch contacts remained open (no signal) during a vehicle deceleration event where braking was clearly occurring based on wheel speed data. This means the brake lights likely did not illuminate when the driver was braking, which is both an electrical fault and a serious safety hazard for following traffic.
Safety Warning
This is a critical safety issue. If the brake lights are not illuminating when braking, following vehicles will not be warned of deceleration, dramatically increasing the risk of rear-end collisions. Additionally, the ABS/ESC system may not function correctly without brake switch input. The vehicle should not be driven at night or in traffic until this is repaired. The fix is usually simple and inexpensive.
Common Causes
35%
Misadjusted or failed brake lamp switch not making contact during pedal depression
25%
Missing or deteriorated brake pedal bumper/pad that positions the switch
20%
Wiring fault in the brake lamp switch circuit (open wire or bad splice)
10%
Blown brake light fuse causing no current flow through the switch circuit
10%
Brake lamp switch connector loose or disconnected
Diagnostic Steps
1
Have an assistant observe the brake lights while you press the pedal — if the lights do not illuminate, the problem is confirmed. Check the brake light fuse first as the simplest cause.
2
Locate the brake lamp switch at the top of the brake pedal arm (under the dash). Check that the rubber bumper/pad that contacts the switch plunger is present and intact — a common failure where the rubber deteriorates and falls off, preventing switch actuation.
3
Test the brake lamp switch with a multimeter — it should show continuity (closed circuit) when the brake pedal is pressed and open when released. If the switch has multiple circuits, test both the brake light circuit and the ABS/cruise circuit separately.
4
If the switch tests good, check for voltage at the switch input (should have battery voltage from the fuse) and output (should have battery voltage only when pedal is pressed). No input voltage indicates a fuse or wiring issue upstream.
5
Inspect for aftermarket modifications to the brake light circuit (trailer wiring, LED conversions) that may have introduced a fault or excessive resistance preventing the ABS module from detecting the switch state.
Estimated Repair Cost
$15 - $150
Parts + labor, varies by vehicle and location
The ABS/ESC module detected that the brake lamp switch contacts remained open (no signal) during a vehicle deceleration event where braking was clearly occurring based on wheel speed data. This means the brake lights likely did not illuminate when the driver was braking, which is both an electrical ...
The most common cause of C1291 (Open Brake Lamp Switch Contacts During Deceleration) is: Misadjusted or failed brake lamp switch not making contact during pedal depression
Typical repair costs for C1291 range from $15 to $150, depending on the vehicle, location, and whether you do it yourself or go to a shop.
This is a critical safety issue. If the brake lights are not illuminating when braking, following vehicles will not be warned of deceleration, dramatically increasing the risk of rear-end collisions. Additionally, the ABS/ESC system may not function correctly without brake switch input. The vehicle should not be driven at night or in traffic until this is repaired. The fix is usually simple and inexpensive.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to C1291 to identify the root cause.
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Quick Info
Category
Chassis
System
Brake System / Vehicle Lighting
Difficulty
Type
Manufacturer
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