Introduction
The B1555 diagnostic trouble code (DTC) indicates a problem within the ignition run/start circuit of a vehicle. This circuit is crucial for providing power to various vehicle systems during both the "run" and "start" positions of the ignition switch. When the engine control unit (ECU) detects a fault in this circuit, it sets the B1555 code, potentially leading to drivability issues or a complete no-start condition. Understanding the causes, symptoms, and troubleshooting steps for this code is essential for proper diagnosis and repair.
Comprehensive Table: B1555 Ignition Run/Start Circuit Failure
| Category | Description | Possible Causes |
|---|---|---|
| Definition | Ignition Run/Start Circuit Failure; Indicates an electrical fault within the circuit responsible for providing power to essential components during the ignition's "run" and "start" positions. | Open circuit in wiring, short to ground, short to voltage, faulty ignition switch, malfunctioning PCM/BCM, corroded connectors/terminals, damaged wiring harness. |
| Symptoms | Noticeable problems related to the operation of the engine and electrical components. | No start condition, engine stalls, intermittent starting problems, inoperative accessories (e.g., radio, wipers), warning lights illuminated (e.g., check engine, battery), reduced engine power, erratic shifting (automatic transmissions). |
| Affected Components | Components that rely on power from the ignition run/start circuit. | Ignition switch, PCM/BCM, starter relay, fuel pump relay, various sensors, ignition coils, injectors, transmission control module (TCM), electronic throttle control (ETC), instrument cluster, body control module (BCM). |
| Diagnostic Tools | Tools needed for diagnosing the B1555 code. | Scan tool (OBD-II scanner), multimeter, test light, wiring diagrams, circuit tester. |
| Troubleshooting Steps | Steps to follow when diagnosing and repairing the B1555 code. | Verify the code, inspect wiring and connectors, test ignition switch, check fuses and relays, test circuit continuity, test circuit voltage, diagnose PCM/BCM. |
| Repair Strategies | Common repair procedures for addressing the B1555 code. | Repair or replace damaged wiring/connectors, replace faulty ignition switch, replace faulty relay, replace faulty PCM/BCM, repair short to ground/voltage. |
| Related DTCs | Other diagnostic trouble codes that might be present alongside the B1555 code. | U0100 (Lost Communication With ECM/PCM), P0685 (ECM/PCM Power Relay Control Circuit Open), P0686 (ECM/PCM Power Relay Control Circuit Low), P0687 (ECM/PCM Power Relay Control Circuit High), B1485 (Ignition 1 Circuit Failure) |
| Severity | The level of impact on the vehicle's operation. | High; Can result in a no-start condition or significant drivability problems. |
| Common Mistakes | Mistakes to avoid during diagnosis and repair. | Failing to inspect wiring thoroughly, misdiagnosing the ignition switch, overlooking corroded connections, replacing the PCM/BCM without proper testing. |
| Wiring Diagram Location | Where to find accurate wiring diagrams for the vehicle. | Vehicle-specific repair manual, online subscription services (e.g., Alldata, Mitchell OnDemand), manufacturer's website. |
| Voltage Testing Locations | Important locations to test voltage when diagnosing B1555. | Ignition switch connector (run/start terminals), PCM/BCM connector (ignition run/start circuit input), relay terminals (power and control circuits). |
| Component Location | General location of key components. | Ignition switch (steering column), PCM/BCM (engine compartment or under the dashboard), relays (fuse box). |
Detailed Explanations
Definition: The B1555 code signifies a malfunction within the ignition run/start circuit. This circuit is responsible for supplying power to various essential vehicle components when the ignition switch is in either the "run" or "start" position. A failure in this circuit disrupts the proper functioning of these components.
Symptoms: Several symptoms can indicate a B1555 code. These include a no-start condition, engine stalling, intermittent starting problems, inoperative accessories (like the radio or wipers), illuminated warning lights (such as the check engine or battery light), reduced engine power, and even erratic shifting in vehicles with automatic transmissions. These symptoms arise because the affected components are not receiving the necessary power from the ignition circuit.
Affected Components: The ignition run/start circuit powers a wide range of components. Key components include the ignition switch itself, the powertrain control module (PCM) or body control module (BCM), the starter relay, the fuel pump relay, various sensors, ignition coils, fuel injectors, the transmission control module (TCM), the electronic throttle control (ETC), the instrument cluster, and other body control modules (BCMs). Any of these components can be affected by a failure in the ignition run/start circuit.
Diagnostic Tools: Diagnosing a B1555 code requires specific tools. A scan tool (OBD-II scanner) is essential for reading the code and viewing related data. A multimeter is necessary for testing voltage and continuity in the circuit. A test light can help identify power and ground issues. Wiring diagrams are crucial for tracing the circuit and identifying components. A circuit tester can also be helpful.
Troubleshooting Steps: A systematic approach is needed for troubleshooting a B1555 code. First, verify the presence of the code using a scan tool. Next, thoroughly inspect the wiring and connectors associated with the ignition run/start circuit for any signs of damage, corrosion, or loose connections. Test the ignition switch to ensure it is functioning correctly. Check fuses and relays related to the circuit. Perform continuity tests on the wiring to identify any open circuits. Test the voltage at various points in the circuit to identify voltage drops or shorts. Finally, if all other possibilities are ruled out, consider the possibility of a faulty PCM/BCM.
Repair Strategies: The repair strategy depends on the underlying cause of the B1555 code. If damaged wiring or connectors are found, they must be repaired or replaced. A faulty ignition switch will require replacement. Faulty relays should also be replaced. If a short to ground or voltage is identified, the cause of the short must be located and repaired. In rare cases, a faulty PCM/BCM may need to be replaced, but this should only be done after all other possibilities have been exhausted.
Related DTCs: The B1555 code may be accompanied by other related DTCs. These include U0100 (Lost Communication With ECM/PCM), P0685 (ECM/PCM Power Relay Control Circuit Open), P0686 (ECM/PCM Power Relay Control Circuit Low), P0687 (ECM/PCM Power Relay Control Circuit High), and B1485 (Ignition 1 Circuit Failure). The presence of these codes can provide additional clues about the nature of the problem.
Severity: The B1555 code is considered a high-severity issue. It can lead to a no-start condition, which prevents the vehicle from being driven. Even if the vehicle starts, significant drivability problems may arise due to the lack of power to essential components.
Common Mistakes: Several common mistakes should be avoided during diagnosis and repair. Failing to thoroughly inspect the wiring is a frequent error. Misdiagnosing the ignition switch is another. Overlooking corroded connections can also lead to incorrect diagnoses. Replacing the PCM/BCM without proper testing is a costly and unnecessary mistake.
Wiring Diagram Location: Accurate wiring diagrams are essential for diagnosing the B1555 code. These diagrams can typically be found in the vehicle-specific repair manual. Online subscription services like Alldata and Mitchell OnDemand also provide access to wiring diagrams. In some cases, the manufacturer's website may offer wiring diagrams as well.
Voltage Testing Locations: When diagnosing a B1555 code, it's important to test the voltage at specific locations. These include the ignition switch connector (at the run/start terminals), the PCM/BCM connector (at the ignition run/start circuit input), and the relay terminals (on both the power and control circuits).
Component Location: The location of key components varies depending on the vehicle make and model. The ignition switch is typically located on the steering column. The PCM/BCM is often found in the engine compartment or under the dashboard. Relays are usually located in the fuse box.
Frequently Asked Questions
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What does the B1555 code mean? The B1555 code indicates a problem in the ignition run/start circuit, which provides power to vital components when the ignition is in the "run" or "start" position.
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What are the common symptoms of a B1555 code? Common symptoms include a no-start condition, engine stalling, and inoperative accessories.
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Can a bad ignition switch cause a B1555 code? Yes, a faulty ignition switch is a common cause of the B1555 code.
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Is the B1555 code a serious problem? Yes, it is considered a serious problem because it can prevent the vehicle from starting or cause significant drivability issues.
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Can I fix a B1555 code myself? Depending on your mechanical skills and access to diagnostic tools, you may be able to diagnose and repair the problem. However, complex electrical issues are often best left to a qualified mechanic.
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What tools do I need to diagnose a B1555 code? You will need a scan tool, a multimeter, a test light, and wiring diagrams.
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How do I test the ignition switch? Using a multimeter, check for voltage and continuity at the ignition switch terminals in the "run" and "start" positions, according to the wiring diagram.
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What should I check first when diagnosing a B1555 code? Start by visually inspecting the wiring and connectors for any signs of damage or corrosion.
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Can a blown fuse cause a B1555 code? Yes, a blown fuse in the ignition run/start circuit can cause the B1555 code.
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How much does it cost to fix a B1555 code? The cost varies depending on the cause of the problem and the labor rates in your area. Replacing an ignition switch typically costs between \$150 and \$400, while PCM/BCM replacement can be significantly more expensive.
Conclusion
The B1555 ignition run/start circuit failure code points to a potentially serious electrical issue that can significantly impact vehicle operation. A methodical approach to diagnosis, utilizing the appropriate tools and wiring diagrams, is crucial for identifying the root cause and implementing the necessary repairs.