B1846 — Ignition Tamper Circuit Open

B1846 — Ignition Tamper Circuit Open. A fault in the ignition system. Short, gentle driving to a shop is usually possible. Typical causes: worn spark plugs or wrong plug gap, damaged coil wiring or connector, faulty ignition control circuit in the ECM.

body electrical

Is it safe to drive?

Drive with caution Drive with caution and avoid load. Ignition faults cause misfires that quickly overheat and destroy the catalytic converter; if the Check Engine Light flashes, stop and fix it first.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm B1846 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many B0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the ignition system for damage, corrosion, chafing or poor contact.
Subsystem check Do a continuity test end-to-end on the ignition tamper circuit and wiggle the harness while measuring — intermittent opens show up as fluctuating readings.
Subsystem check Swap the coil to another cylinder and see if the fault code follows it.
Subsystem check Inspect spark plugs for wear, oil or carbon tracks and check plug gaps.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm B1846 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for B1846 (parts and labor, USD, independent shop rates): Replace spark plugs: $90–$250; Replace an ignition coil: $150–$380; Repair coil wiring or connector: $80–$250. Overall, fixing B1846 usually costs between $80 and $380. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

Is it safe to drive with B1846?

Drive with caution and avoid load. Ignition faults cause misfires that quickly overheat and destroy the catalytic converter; if the Check Engine Light flashes, stop and fix it first.

What does OBD2 code B1846 mean?

How do I diagnose B1846 myself?

Start with a scan: confirm B1846, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the ignition tamper, and verify the suspect component against live data before buying parts.

How much does it cost to fix B1846?

Replace spark plugs — $90–$250; Replace an ignition coil — $150–$380; Repair coil wiring or connector — $80–$250. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

What are the symptoms of B1846?

Drivers most often notice: increased fuel consumption, hard starting, especially in damp weather, Check Engine Light on, misfires under load or at idle.

The engine control module logs code B1846 when it finds a problem with the ignition tamper circuit. This falls under the body electrical category of OBD2 codes, which means the issue isn't directly related to engine mechanicals but rather to the electrical monitoring systems that watch over how the ignition operates. When the module sets B1846, it's telling you that an expected electrical signal is missing from the ignition tamper circuit entirely.

"Circuit open" is the key phrase here. It means the electrical path that the control module expects to see has been interrupted somewhere along the way. Current cannot flow through a broken circuit, so the module registers this as a fault. Typical culprits include severed wires in the harness, connectors that have come loose or developed corrosion at their pins, a fuse that has blown, or a component that has failed internally and no longer passes electricity.

The module does not set B1846 after a single bad reading. It monitors this circuit throughout normal driving and only stores the code after the fault persists for a set number of drive cycles. When that happens, the Check Engine Light illuminates and freeze frame data gets saved automatically. That snapshot records engine rpm, load, temperature, and vehicle speed at the exact moment the module detected the problem. You can pull this data with any decent OBD2 scanner, and it tells you exactly what conditions triggered the fault — invaluable information for tracking down intermittent issues.

Common symptoms of B1846

The Check Engine Light stays illuminated on the dashboard
Engine misfires occur either at idle or under acceleration load
Noticeable loss of engine power with jerking or stuttering during throttle input
Hard starting, particularly when the weather is damp or humid
Fuel consumption climbs noticeably higher than your normal average
Rough idle or unstable engine running

What causes B1846?

The ignition tamper circuit can fail for several reasons, ranging from simple wiring problems to complete component failure:

A broken or severed wire somewhere in the ignition tamper harness is the most frequent cause
The ignition tamper switch or sensor itself has failed internally and no longer completes the circuit
A fuse that supplies power to the ignition tamper circuit has blown due to an overload or short
A connector is unplugged, has a pin that backed out of its socket, or shows heavy corrosion buildup
Spark plugs are worn out, coated with oil or carbon deposits, or have the wrong gap setting
Moisture or engine oil has entered the spark plug tube wells, shorting the secondary ignition circuit
Wiring or connectors related to the ignition coil are damaged, melted, or loose
The ignition coil or coil pack has failed outright

How to diagnose B1846

Follow a systematic approach to avoid replacing good parts:

Plug in an OBD2 scanner and confirm B1846 is stored in the module memory. Save the freeze frame data before clearing anything — this record shows the precise engine conditions present when the fault first appeared.
Check for any other stored trouble codes. Related codes often point to the root cause rather than just the symptom. Also look up any technical service bulletins for your specific make and model; manufacturers sometimes publish known fixes or software updates for recurring B1846 complaints.
Perform a thorough visual inspection of all wiring and connectors tied to the ignition tamper circuit. Look for chafed insulation, burned spots, corrosion at the terminals, and any wires that have pulled free from their connectors.
Use a multimeter to check continuity through the entire ignition tamper circuit from end to end. While measuring, wiggle and flex the harness — if the reading fluctuens or goes infinite intermittently, you have found an open circuit that moves when the vehicle does.
If available, swap the suspect ignition coil with one from another cylinder. Clear the code and see if B1846 moves with the coil to a different cylinder, which confirms the coil as the problem.
Remove and inspect all spark plugs. Check for worn electrodes, oil fouling, carbon tracking, and incorrect gap. Replace any plugs that look questionable.
Clear the code, complete a drive cycle that reproduces the conditions from the freeze frame data, and verify that B1846 does not return.

Repair options and costs

Once you have identified the failed component, repairs typically involve one of the following:

Spark plug replacement: $90–$250
Ignition coil or coil pack replacement: $150–$380
Wiring harness or connector repair: $80–$250

Total repair cost for B1846

The final bill depends entirely on what part is actually faulty. Most B1846 repairs fall between $80 and $380 when you include both parts and labor at independent shop rates. Always spend time diagnosing before buying parts. The ignition coil is the most expensive single component, but it is rarely the first thing to check. Starting with visual inspection and basic testing saves money and prevents unnecessary parts purchases.

Can you drive with B1846?

This code warrants caution. Ignition-related faults cause engine misfires, and unburned fuel entering the exhaust system can overheat and destroy the catalytic converter in short order. Drive conservatively and avoid heavy loads or hard acceleration. If the Check Engine Light begins flashing rather than staying solid, stop driving immediately — a flashing CEL indicates an active misfire that requires immediate attention.