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Home / DTC / B2278 — Engine/Power Switch Malfunction

B2278 — Engine/Power Switch Malfunction

Detailed page for trouble code B2278.

34,405codes
59brands
11,914generic
22,491specific
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Code

B2278

LEXUS B — Body

Engine/Power Switch Malfunction

Brand: LEXUS
Type: B — Body
AI status
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Completed 100%
Page language: EN

Causes

  • Faulty engine/power (start/stop) switch assembly
  • Damaged wiring, short to power or ground, or open circuit between switch and body ECU
  • Poor or corroded connectors at the switch or body ECU
  • Intermittent CAN/LIN communication fault between switch module and body ECU
  • Blown fuse or poor battery/low system voltage
  • Software/firmware glitch or needed reprogramming

Symptoms

  • Push‑button start/stop does not respond or requires multiple presses
  • Vehicle does not enter ACC/ON/START modes reliably
  • START/STOP or accessory functions intermittent
  • Warning lamp or message about the power/engine switch
  • Engine fails to crank despite correct key detection
  • Inconsistent behavior when pressing the switch (lags, repeated presses)

What to check

  • Scan for additional trouble codes and freeze-frame data; record related U and P codes
  • Visually inspect switch, wiring harness, and connectors for damage, corrosion, or moisture
  • Check battery voltage and charging system; ensure battery terminals are clean and tight
  • Verify fuses and fusible links related to the power switch and body ECU circuits
  • Operate the switch while monitoring inputs at the body ECU (voltage/signals) and watch for changes
  • Check for lost or intermittent CAN/LIN bus messages using a diagnostic tool

Signal parameters

  • Battery voltage at switch (should be ~12.6 V at rest, >11 V during cranking)
  • Switch output signal to body ECU (digital high/low or open/closed states when pressed)
  • Resistance or continuity across switch terminals (per service spec)
  • CAN/LIN network message presence and content (switch status messages)
  • Ground continuity for switch and module grounds
  • Voltage at related fuse circuits and ECU input pins

Diagnostic algorithm

  1. Retrieve all stored codes, freeze frame, and live data. Note any related U or P codes.
  2. Verify battery condition and charging system; correct low-voltage conditions before further testing.
  3. Visually inspect the push‑button switch, harness, and connector for damage, corrosion, or water ingress.
  4. Check relevant fuses and fusible links; replace if blown and retest.
  5. With a multimeter, probe the switch connector while operating the switch: verify expected voltages, continuity, and switching behavior per wiring diagram.
  6. Backprobe the body ECU input pin for the switch and confirm signal arrives and changes state when the switch is pressed.
  7. Perform wiggle/torque tests on connectors and harnesses while monitoring live data to identify intermittent faults.
  8. Use a scan tool to monitor CAN/LIN traffic for missing or malformed messages from the switch/module; repair bus faults if present.
  9. If wiring and signals are good, replace the push‑button switch assembly and recheck.
  10. If fault persists after switch replacement, consider body ECU or related module failure — consult manufacturer diagnostic flow, update/reflash software if available, and replace module only after confirming.

Likely causes

  • Wiring/connectors at the engine/power switch (most common)
  • Faulty push‑button switch assembly
  • Low battery voltage or poor battery terminal connection
  • Body ECU detecting invalid or missing communication messages
  • Internal switch contamination or sticking contacts

Fault status

⚠️ Status
Malfunction detected in Engine/Power (push‑button) switch circuit or related control/communication.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

B2276 B2277 B2280 U0073 U0140 P0562
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