Code
B29EB
MITSUBISHI
B — Body
Key switch signal:open cycle
Views:
UK: 9
EN: 11
RU: 11
AI status
Completed
Completed
100%
Causes
- Open or intermittent wiring in key switch/ignition switch circuit
- Corroded, loose or damaged connector at key switch or BCM/ECU
- Faulty ignition/key switch or mechanical key cylinder
- Poor ground or battery/low voltage condition affecting the signal
- Faulty body control module (BCM) / immobilizer / instrument cluster input
- Short to power or ground on the key switch signal circuit
Symptoms
- Intermittent or no response when turning key (no crank or accessory power)
- Starter does not engage or engages unpredictably
- Accessories (radio, dash lights) not powered in expected key positions
- Security/immobilizer warning lamp illuminated or flashing
- Random no-starts or stalls immediately after key turn
- DTC present and stored in BCM/ECU
What to check
- Visually inspect ignition key switch, steering column area and connectors for damage or corrosion
- Scan for additional DTCs (immobilizer, BCM, communication codes) and capture freeze frame data
- Monitor key/ignition switch input signal with a scan tool or oscilloscope while operating the key through OFF/ACC/ON/START
- Perform wiggle test on wiring and connectors while observing signal or symptoms
- Check battery voltage and main grounds; verify stable supply voltage during tests
- Measure continuity/resistance of the wiring between key switch and BCM; check for shorts to power/ground
Signal parameters
- Key switch output is a discrete open/closed signal referenced to vehicle ground (expected to switch between ~0 V and battery voltage when closed)
- Signal should change cleanly and consistently when key moved through OFF → ACC → ON → START positions
- No prolonged open or intermittent pulses during a normal key cycle
- If using an oscilloscope, expect clean transitions with minimal bouncing; repeated open pulses indicate intermittent contact
Diagnostic algorithm
- Read and record all stored DTCs and freeze frame data. Note relevant time, battery voltage and vehicle state.
- Attempt to reproduce the fault while monitoring the key switch signal with a scan tool or lab scope. Verify pattern and timing of open/closed transitions.
- Perform visual inspection of ignition switch, key cylinder, connector pins and harness near steering column for damage, corrosion or signs of repair.
- Check battery voltage and main grounds. Repair any low-voltage or grounding issues before continuing.
- With the ignition OFF and battery disconnected, check continuity between the key switch connector and the BCM/input pin to identify opens. Also check for shorts to battery/ground.
- With power applied, backprobe the key switch connector and measure voltage while cycling key positions. Confirm expected voltage levels and clean transitions.
- If intermittent is present, wiggle harness/connectors while monitoring the signal to locate a break. Repair or replace damaged wiring/connector.
- If wiring and connectors are good, replace the ignition/key switch assembly. Retest the key cycle signal after replacement.
- If problem persists after switch replacement, test or replace the receiving module (BCM/immobilizer/input module) or inspect for aftermarket device conflicts.
- Clear codes and perform final verification: multiple key cycles without recurrence of the DTC and restored normal operation.
Likely causes
- Corroded or loose connector at the ignition/key switch
- Broken or chafed wire in harness near steering column
- Failing ignition switch (internal contacts worn or intermittent)
- Poor ground at the BCM or ignition switch
- Intermittent BCM/input module fault
Fault status
Status
Open-cycle detected on key/ignition switch signal circuit — input did not provide the expected closed transitions during a monitored key cycle. Possible open, intermittent connection, or faulty ignition switch/module.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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