B1845

Ignition Tamper Circuit Failure

Body Chassis/Safety Anti-Theft/Security 🟢 Low — Fix at next service ✅ Safe to Drive
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What This Actually Means

In plain language — no jargon

Your vehicle's security system detected a problem with the ignition tamper detection circuit, similar to a door alarm sensor that's malfunctioning. This circuit monitors whether someone is trying to bypass or manipulate the ignition switch.

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Symptoms You May Notice

3 known symptoms for this code
Check Engine Light or Security warning light illuminated
Vehicle may not start or starts intermittently
Steering wheel lock may not engage or disengage properly
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECU monitors voltage and signal integrity from the ignition tamper switch circuit, which detects unauthorized ignition manipulation attempts. The circuit expects a clean digital signal transitioning between high and low states at the ignition switch. A fault occurs when voltage remains stuck, signals are erratic, or the circuit shows open/short conditions.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Ignition Tamper Signal Voltage 0V (off) or 12V (on) with clean transitions Stuck voltage, noise, or no signal detected
Signal Response Time <100ms transition between states >500ms or no response to ignition position changes
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Battery terminals and connections
Clean battery terminals and tighten cable connections to ensure proper voltage supply to the security module.
2
Ignition switch wiring harness
Inspect the wiring harness connected to the ignition switch for loose connectors, corrosion, or damaged pins and reseat connections.
3
Ignition switch assembly
Replace the ignition switch if wiring checks pass, as internal switch contacts may be worn or corroded.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code B1845 is a low-severity fault. Your vehicle is generally safe to drive to a workshop for diagnosis. However, do not ignore it indefinitely — low-severity codes often indicate developing problems that become expensive if neglected. Book a diagnostic appointment within 2–4 weeks. If you notice any additional symptoms (rough running, power loss, unusual smells), treat it as higher priority.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.
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How to Clear Code B1845

What happens after you fix the fault

Once the fault is repaired, B1845 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When
  • Fault has been diagnosed and repaired
  • You want to confirm the repair worked
  • Code appeared after a sensor was cleaned
⚠️ Do Not Clear When
  • Preparing for an emissions/PUC test
  • Root cause is still undiagnosed
  • Check engine light is flashing
Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.