Brake Light Switch Failure

Symptoms

• Random, brief power loss or sudden loss of acceleration, sometimes occurring multiple times within a short distance [3, 4]
• ABS, ESP, Traction Control, and BRAKE warning lights illuminating on the dash with no other obvious symptoms [2]
• Engine cuts power when the brake pedal is touched while still on the accelerator [0]
• Fault code logged as 'Brake signal: Plausibility' [1]
• Fault code P-1926 associated with brake switch plausibility issues [10]
• Intermittent symptoms — some days the problem does not occur, other days it repeats frequently [3]

Causes

• The brake switch intermittently floats between on and off states, sending conflicting signals to the ECU [4]
• The ECU interprets simultaneous throttle and brake signals as a plausibility fault, cutting engine power [0, 1]
• A faulty brake switch can trigger false ABS/ESP warning lights because the brake signal feeds into those systems [1, 2]
• Physical wear or deterioration of the switch mechanism over time causes unreliable contact [7]

Diagnosis

• Perform a moving test: hold the accelerator and lightly touch the brake pedal at the same time — if this reproduces the power-loss symptom, the brake switch is the likely culprit [0]
• Check whether the brake lights are functioning correctly; erratic or always-on brake lights point to the switch [1]
• Scan for fault codes — a 'Brake signal: Plausibility' fault or P-1926 code strongly suggests a brake switch issue [1, 10]
• Note that a failing brake switch may not always store a fault code, so the absence of codes does not rule it out [0]
• Check for ABS-related faults as well — a failing wheel speed sensor or mismatched tire sizes can produce similar plausibility errors and should be ruled out [1]

Repair

The brake light switch (referred to in the WIS as the stop lamp switch) is mounted on the brake pedal bearing bracket and connects via a plug connector [8]. Replacement is straightforward and inexpensive — owners report the part costs around $15 [7]. The main challenge is physically releasing the switch from its mounting clip, which requires pressing a tab to free it [6]. Most owners with basic mechanical confidence can complete this job in under an hour.

Parts

Plain part names — affiliate links and pricing are coming in a later update.

• Brake light switch / stop lamp switch (approximately $15, OEM or aftermarket) [7]

Related forum threads

• 19 ↳10 Year Member with Mystery Problem--A little help please
• 19 ↳Random T1N acceleration problem
• 19 ↳Random, brief power loss?!
• 19 ↳T1N Brake Switch Wiring
• 19 ↳Recurring Limp Mode only code is P-1926

From the manuals

• Workshop manual (2000–2003)

  "Petroleum based fluids would be items such as engine oil, transmission fluid, power steering fluid, etc. Fig. 13 FLUID LEVEL TYPICAL 1 - FLUID RESERVOIR 2 - MAX LEVEL MARK 5 - 14BRAKES - BASEVA DISC BRAKE CALIPER ADAPTER (Continued) FLUID RESERVOIR REMOVAL (1) Using a suction gun remove as much brake fluid from the reservoir as possible (Fig. 14). (2) Disconnect the electrical connector for the brake fluid level indicator (Fig. 14). (3) Remove the fluid reservoir (Fig. 14).Seal off the ends and bore holes with plugs. INSTALLATION (1) Install the fluid reservoir and fill with fluid (Fig. 14). ("

• Workshop manual (2000–2003)

  "It is not possible to repair the master cylinder. INSTALLATION (1) Install the master cylinder to the brake booster (Fig. 20). Tighten to 28 N·m (248 in. lbs.). (2) Install the brake lines (Fig. 20). Tighten to 14 N·m (124 in. lbs.). (3) Install the fluid reservoir (Fig. 20) (Refer to 5 - BRAKES/HYDRAULIC/MECHANICAL/FLUID RESERVOIR - INSTALLATION). (4) Bleed the brake system. (5) Check the brake system for any leaks. PEDAL REMOVAL (1) Remove the master cylinder (Refer to 5 - BRAKES/HYDRAULIC/MECHANICAL/MASTER CYLINDER - REMOVAL). (2) Remove the retainer and pin for the master cylinder push rod"

• Workshop manual (2004–2006)

  "If the approved product is not available, use a DOT 4 brake fluid: minimum dry boiling point (ERBP) 500°F, minimum wet boiling point (WERBP) 356°F, maximum viscosity 1500 mm 2 /s, conforming to FMVSS 116 and ISO 4925. No other type of brake fluid is recommended or approved for usage in the vehicle brake system. Use only approved brake fluid or an equivalent from a tightly sealed container. Use brake fluid 5-14 BRAKES-BASEVA CAUTION: Never use reclaimed brake fluid or fluid from an container which has been left open. An open container of brake fluid will absorb moisture from the air and contami"

Sources