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Home / DTC / B1704 — Auto light sensor open

B1704 — Auto light sensor open

Detailed page for trouble code B1704.

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Code

B1704

MITSUBISHI B — Body

Auto light sensor open

Brand: MITSUBISHI
Type: B — Body
Views: UK: 8 EN: 13 RU: 13
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Disconnected or loose sensor connector
  • Broken / chafed wiring harness or open conductor between sensor and BCM
  • Corroded or bent terminal in connector
  • Failed/defective ambient (auto) light sensor
  • Water intrusion or contamination at sensor or connector
  • Blown fuse or related power/ground fault upstream

Symptoms

  • Automatic headlamp function not working (won't switch on/off automatically)
  • Interior/auto-dimming features may not respond correctly
  • Dashboard or warning lamp related to lighting/illumination may appear
  • Lights stuck in manual state (always on or always off)
  • Intermittent operation of auto lights depending on movement or vibration

What to check

  • Use a diagnostic scanner to read the freeze frame and confirm the B1704 code and any related codes
  • Visually inspect the sensor location (usually on dash top or near windshield), its connector and wiring for damage, corrosion or water intrusion
  • Check fuses and related power/ground circuits for the lighting/BCM
  • Backprobe the sensor connector and measure reference voltage with ignition ON
  • Measure sensor signal voltage while changing ambient light (cover/uncover sensor) to see if signal varies
  • Perform continuity check between sensor signal/ground pins and the BCM connector

Signal parameters

  • Reference supply: typically a regulated reference (commonly around 5 V) from BCM — verify against vehicle wiring diagram
  • Signal output: variable voltage expected within 0–5 V range depending on light level (dark = low voltage, bright = higher voltage) — open circuit shows no change or out-of-range reading
  • Open-circuit indication: infinite resistance / no continuity or signal stuck at supply rail or 0 V
  • Resistance: sensor element typically shows variable resistance with light; open = very high/OL

Diagnostic algorithm

  1. Connect a scan tool and confirm stored codes, freeze frame and live data for the ambient light sensor input.
  2. Visually inspect sensor, mounting, and harness for obvious damage, corrosion, or water entry. Repair any visible issues.
  3. With ignition ON (engine off), backprobe the sensor connector. Verify reference voltage present at the supply pin (consult service manual for pinout). If no reference, inspect upstream fuses/BCM power.
  4. Measure signal pin voltage while changing light on the sensor (cover/uncover). Expected: signal varies. If it does vary, the sensor and wiring are likely OK; if not, continue.
  5. Check continuity between sensor ground and chassis ground, and between sensor signal pin and corresponding BCM input pin. Repair any open circuits.
  6. Inspect connector terminals for corrosion or poor contact; clean or replace connector as required and apply dielectric grease if appropriate.
  7. If wiring and connector are good but sensor signal does not change, remove and bench-test or replace the ambient light sensor.
  8. If new sensor still shows open or no signal, suspect BCM input fault — verify with wiring diagrams and consider testing at BCM connector or consult OEM procedures before replacing BCM.
  9. After repairs, clear codes and verify proper operation of auto lighting over several ignition cycles and changing light conditions.

Likely causes

  • Connector unplugged or poorly seated at the sensor
  • Damaged wire (pinched, chafed, or broken) in the harness to the sensor
  • Corrosion or bent pins inside the sensor connector
  • Failed ambient light sensor element

Fault status

⚠️ Status
Ambient (auto) light sensor circuit open — no valid signal detected by the body control module.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-1.5 hours

Similar codes

B1700 B1701 B1702 B1703 B1705 B1706
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Code

B1704

Other B — Body

Seat Driver Recline Forward Switch Circuit Short To Ground

Brand: Other
Type: B — Body
Views: UK: 15 EN: 25 RU: 19
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Disconnected or loose sensor connector
  • Broken / chafed wiring harness or open conductor between sensor and BCM
  • Corroded or bent terminal in connector
  • Failed/defective ambient (auto) light sensor
  • Water intrusion or contamination at sensor or connector
  • Blown fuse or related power/ground fault upstream

Symptoms

  • Automatic headlamp function not working (won't switch on/off automatically)
  • Interior/auto-dimming features may not respond correctly
  • Dashboard or warning lamp related to lighting/illumination may appear
  • Lights stuck in manual state (always on or always off)
  • Intermittent operation of auto lights depending on movement or vibration

What to check

  • Use a diagnostic scanner to read the freeze frame and confirm the B1704 code and any related codes
  • Visually inspect the sensor location (usually on dash top or near windshield), its connector and wiring for damage, corrosion or water intrusion
  • Check fuses and related power/ground circuits for the lighting/BCM
  • Backprobe the sensor connector and measure reference voltage with ignition ON
  • Measure sensor signal voltage while changing ambient light (cover/uncover sensor) to see if signal varies
  • Perform continuity check between sensor signal/ground pins and the BCM connector

Signal parameters

  • Reference supply: typically a regulated reference (commonly around 5 V) from BCM — verify against vehicle wiring diagram
  • Signal output: variable voltage expected within 0–5 V range depending on light level (dark = low voltage, bright = higher voltage) — open circuit shows no change or out-of-range reading
  • Open-circuit indication: infinite resistance / no continuity or signal stuck at supply rail or 0 V
  • Resistance: sensor element typically shows variable resistance with light; open = very high/OL

Diagnostic algorithm

  1. Connect a scan tool and confirm stored codes, freeze frame and live data for the ambient light sensor input.
  2. Visually inspect sensor, mounting, and harness for obvious damage, corrosion, or water entry. Repair any visible issues.
  3. With ignition ON (engine off), backprobe the sensor connector. Verify reference voltage present at the supply pin (consult service manual for pinout). If no reference, inspect upstream fuses/BCM power.
  4. Measure signal pin voltage while changing light on the sensor (cover/uncover). Expected: signal varies. If it does vary, the sensor and wiring are likely OK; if not, continue.
  5. Check continuity between sensor ground and chassis ground, and between sensor signal pin and corresponding BCM input pin. Repair any open circuits.
  6. Inspect connector terminals for corrosion or poor contact; clean or replace connector as required and apply dielectric grease if appropriate.
  7. If wiring and connector are good but sensor signal does not change, remove and bench-test or replace the ambient light sensor.
  8. If new sensor still shows open or no signal, suspect BCM input fault — verify with wiring diagrams and consider testing at BCM connector or consult OEM procedures before replacing BCM.
  9. After repairs, clear codes and verify proper operation of auto lighting over several ignition cycles and changing light conditions.

Likely causes

  • Connector unplugged or poorly seated at the sensor
  • Damaged wire (pinched, chafed, or broken) in the harness to the sensor
  • Corrosion or bent pins inside the sensor connector
  • Failed ambient light sensor element

Fault status

⚠️ Status
Ambient (auto) light sensor circuit open — no valid signal detected by the body control module.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-1.5 hours

Similar codes

B1700 B1701 B1702 B1703 B1705 B1706
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