What Does The 51ae BMW Code Actually Mean?

The 51ae Bmw Code signifies a fault related to the brake signal transmitter via the Controller Area Network (CAN) bus. Resolving this issue promptly by diagnosing the brake system, CAN bus, and related components will help ensure safe vehicle operation, prevent further complications, and maintain optimal performance.

1. What Triggers the 51AE BMW Code & How to Fix it?

The 51AE BMW code indicates a fault related to the brake signal transmitter via the CAN bus. This means the car’s computer (ECU) isn’t receiving the correct brake signal information. Understanding the root causes and diagnostic steps is crucial for effective troubleshooting and repair.

1.1 Potential Causes of the 51AE BMW Code

Several factors can trigger the 51AE code. Here’s a breakdown:

• Faulty Brake Light Switch: The brake light switch, usually located near the brake pedal, is responsible for sending a signal when the brakes are applied. If this switch is malfunctioning, it can send an incorrect signal or no signal at all.
• Wiring Issues: Damaged, corroded, or loose wiring in the brake light circuit or CAN bus can disrupt the signal transmission.
• CAN Bus Problems: The CAN bus is a network that allows different electronic control units (ECUs) in the car to communicate. Problems with the CAN bus itself can interfere with the brake signal.
• Faulty ECU: Although less common, a malfunctioning ECU can misinterpret or fail to receive the brake signal.
• Software Glitches: Software issues within the ECU or other modules can sometimes trigger false codes.
• Low Battery Voltage: Insufficient voltage can sometimes cause erratic behavior in electronic components.

1.2 Diagnostic Steps for the 51AE BMW Code

A systematic approach to diagnosing the 51AE code will help pinpoint the problem. Here’s a step-by-step guide:

1. Read the Codes: Use an OBD-II scanner to confirm the 51AE code and check for any other related codes.
2. Inspect the Brake Light Switch:
   • Check the switch for physical damage.
   • Test the switch’s operation with a multimeter. It should show continuity when the brake pedal is pressed and no continuity when released.
   • Ensure the switch is properly adjusted.
3. Check Wiring and Connectors:
   • Visually inspect the wiring and connectors associated with the brake light switch and CAN bus for damage, corrosion, or looseness.
   • Use a multimeter to check for continuity and voltage in the wiring.
   • Pay special attention to ground connections.
4. Inspect the CAN Bus:
   • Use an oscilloscope to check the CAN bus signal for proper waveform and voltage levels.
   • Look for any breaks or shorts in the CAN bus wiring.
5. Check the ECU:
   • Inspect the ECU connectors for corrosion or damage.
   • If possible, try swapping the ECU with a known good unit to see if the problem is resolved (this should be done by a qualified technician).
6. Check Battery Voltage: Ensure the battery voltage is within the specified range. Low voltage can cause various electrical issues.

1.3 Repair Procedures for the 51AE BMW Code

Once you’ve identified the cause, you can proceed with the repair. Here are some common solutions:

• Replace the Brake Light Switch: If the brake light switch is faulty, replace it with a new one. Ensure it’s properly adjusted after installation.
• Repair Wiring Issues: Repair any damaged or corroded wiring. Replace any broken connectors. Ensure all connections are clean and tight.
• Address CAN Bus Problems:
  • Repair or replace any damaged CAN bus wiring.
  • If a specific module on the CAN bus is causing interference, troubleshoot and repair or replace that module.
• ECU Repair or Replacement: If the ECU is faulty, it may need to be repaired or replaced. This is a complex procedure that should be done by a qualified technician.
• Software Update: Sometimes, a software update from BMW can resolve the issue. Check with your dealer to see if an update is available.
• Charge or Replace the Battery: If the battery voltage is low, charge the battery or replace it if it’s no longer holding a charge.

Alternative text: A detailed BMW ECU wiring diagram, highlighting various connections and components within the system, useful for diagnosing electrical issues.

1.4 Common Mistakes to Avoid

• Assuming the Brake Light Switch is Always the Problem: While a faulty brake light switch is a common cause, it’s essential to perform a thorough diagnosis to rule out other possibilities.
• Neglecting Wiring Issues: Wiring problems can be difficult to find, but they can cause a variety of issues. Don’t overlook the importance of inspecting the wiring and connectors.
• Ignoring the CAN Bus: The CAN bus is a critical part of the car’s electrical system. If you’re having trouble diagnosing the problem, it’s essential to check the CAN bus for proper operation.
• Not Clearing the Codes: After performing the repair, clear the codes with an OBD-II scanner and test drive the car to make sure the problem is resolved.

2. Comprehensive List of BMW Fault Codes Related to Braking System

Understanding related codes can provide a broader picture when diagnosing the 51AE BMW code.

Code	Description	Possible Causes
51AE	Brake signal transmitter CAN	Faulty brake light switch, wiring issues, CAN bus problems, faulty ECU
5E20	Hydraulic pressure sensor	Faulty hydraulic pressure sensor, wiring issues, ABS module failure
5E15	CAN bus: Data fault from DSC control unit	CAN bus problems, faulty DSC control unit
D35A	No message from brake light switch	Faulty brake light switch, wiring issues, CAN bus problems
6131	Power supply too low during brake actuation	Low battery voltage, faulty alternator, wiring issues
5F77	Brake light switch implausible signal	Faulty brake light switch, wiring issues, ABS module failure
5E24	Pressure sensor offset test failed	Faulty pressure sensor, air in brake lines, ABS module failure
6146	Undervoltage while braking	Low battery, alternator issues, high electrical load during braking
6147	Overvoltage while braking	Voltage regulator issue, alternator overcharging
5DC0	Wheel speed sensor front right: implausible signal	Faulty wheel speed sensor, wiring issues, ABS module failure, damaged wheel bearing
5DA0	Wheel speed sensor front left: implausible signal	Faulty wheel speed sensor, wiring issues, ABS module failure, damaged wheel bearing
5DE0	Wheel speed sensor rear right: implausible signal	Faulty wheel speed sensor, wiring issues, ABS module failure, damaged wheel bearing
5D80	Wheel speed sensor rear left: implausible signal	Faulty wheel speed sensor, wiring issues, ABS module failure, damaged wheel bearing
6143	Brake light activation – Short circuit to positive or open circuit	Wiring issues, faulty brake light bulbs, faulty brake light switch
6144	Brake light activation – Short circuit to ground	Wiring issues, short circuit in brake light circuit
6145	Brake force display – Short circuit to positive or open circuit	Wiring issues, faulty brake force display module
6142	Brake force display – Short circuit to ground	Wiring issues, short circuit in brake force display circuit
5E0A	Steering angle sensor signal invalid	Faulty steering angle sensor, wiring issues, DSC module failure
5E43	Steering angle sensor, internal fault	Faulty steering angle sensor, DSC module failure
5E30	Yaw rate sensor signal invalid	Faulty yaw rate sensor, wiring issues, DSC module failure
5E31	Yaw rate sensor, internal fault	Faulty yaw rate sensor, DSC module failure
5DF0	Hydraulic unit pump motor faulty	Faulty ABS pump motor, wiring issues, ABS module failure
5DF1	Hydraulic unit pump motor supply voltage faulty	Low voltage to ABS pump motor, wiring issues, ABS module failure
5E50	Valve relay faulty	Faulty valve relay, wiring issues, ABS module failure
5E51	Valve relay activation faulty	Wiring issues, ABS module failure
5F30	DSC sensor supply voltage faulty	Low voltage to DSC sensors, wiring issues, DSC module failure
5F31	DSC sensor supply voltage too high	High voltage to DSC sensors, voltage regulator issue, DSC module failure
5F40	DSC control unit faulty	Internal DSC control unit failure
5F41	DSC control unit EEPROM faulty	Corrupted EEPROM in DSC control unit
5F42	DSC control unit coding faulty	Incorrect coding in DSC control unit
5F43	DSC control unit variant coding faulty	Incorrect variant coding in DSC control unit
5F50	DSC control unit reset faulty	Internal DSC control unit reset failure
5F51	DSC control unit watchdog faulty	Internal DSC control unit watchdog failure
5F52	DSC control unit RAM faulty	Internal DSC control unit RAM failure
5F53	DSC control unit ROM faulty	Internal DSC control unit ROM failure
5F60	Steering angle sensor adaptation faulty	Steering angle sensor adaptation not performed or failed
5F61	Steering angle sensor calibration faulty	Steering angle sensor calibration not performed or failed
5F70	Brake light switch signal faulty or not plausible	Faulty brake light switch, wiring issues, ABS module failure
5F71	Brake light switch signal implausible	Faulty brake light switch, wiring issues, ABS module failure
5F72	Brake light switch signal not plausible during test routine	Faulty brake light switch, wiring issues, ABS module failure
5F73	Brake light switch signal implausible during test routine	Faulty brake light switch, wiring issues, ABS module failure
5F74	Brake light switch signal implausible during driving	Faulty brake light switch, wiring issues, ABS module failure
5F75	Brake light switch signal implausible during braking	Faulty brake light switch, wiring issues, ABS module failure
5F76	Brake light switch signal implausible during ABS intervention	Faulty brake light switch, wiring issues, ABS module failure

3. How CAN Bus System Works?

The CAN bus (Controller Area Network) is a robust communication network that allows various electronic control units (ECUs) within a vehicle to communicate with each other without a central host computer. It is essential for modern automotive systems.

3.1 Key Features of the CAN Bus

• Decentralized Communication: Unlike traditional systems where a central computer controls all communication, the CAN bus allows each ECU to communicate directly with other ECUs.
• High Speed: The CAN bus operates at high speeds, allowing for real-time data transmission.
• Robustness: The CAN bus is designed to be resistant to interference and noise, making it suitable for the harsh automotive environment.
• Flexibility: The CAN bus can be easily expanded to accommodate new ECUs and functions.
• Cost-Effectiveness: By reducing the amount of wiring required, the CAN bus helps to reduce the cost and weight of the vehicle.

3.2 Components of a CAN Bus System

• Electronic Control Units (ECUs): These are the computers that control various functions in the vehicle, such as the engine, transmission, brakes, and airbags. Each ECU has a CAN controller that allows it to communicate on the CAN bus.
• CAN Controller: This is a specialized microcontroller that handles the communication protocol on the CAN bus. It is responsible for sending and receiving messages.
• CAN Transceiver: This is a physical layer interface that converts the digital signals from the CAN controller into electrical signals that can be transmitted over the CAN bus wires.
• CAN Bus Wires: These are the wires that connect all the ECUs together. The CAN bus typically uses two wires: CAN High (CANH) and CAN Low (CANL).
• Terminating Resistors: These resistors are placed at each end of the CAN bus to prevent signal reflections and ensure proper communication.

3.3 How Data is Transmitted on the CAN Bus

1. Message Prioritization: Each message on the CAN bus has a unique identifier that indicates its priority. Higher priority messages are transmitted first.
2. Message Arbitration: If two or more ECUs try to transmit a message at the same time, the CAN bus uses a process called arbitration to determine which message gets transmitted first. The ECU with the highest priority message wins the arbitration.
3. Data Transmission: Once the arbitration is complete, the winning ECU transmits its message onto the CAN bus. The message consists of an identifier, data, and error-checking information.
4. Message Reception: All ECUs on the CAN bus listen for messages. When an ECU receives a message that is relevant to it, it processes the data.
5. Error Detection: The CAN bus includes error-detection mechanisms to ensure that messages are transmitted correctly. If an error is detected, the message is retransmitted.

3.4 Common CAN Bus Problems

• Wiring Issues: Damaged, corroded, or loose wiring can disrupt communication on the CAN bus.
• ECU Failures: A malfunctioning ECU can interfere with CAN bus communication.
• Terminating Resistor Problems: If the terminating resistors are not functioning correctly, it can cause signal reflections and communication errors.
• Software Issues: Software glitches within the ECUs can sometimes cause CAN bus problems.

Alternative text: An automotive CAN bus system diagram illustrating interconnected ECUs, CAN controllers, transceivers, and terminating resistors for effective vehicle communication.

4. Diagnosing CAN Bus Issues

Diagnosing CAN bus issues requires specialized tools and knowledge. Here are some common diagnostic techniques:

• Visual Inspection: Check the wiring and connectors for damage, corrosion, or looseness.
• Multimeter Testing: Use a multimeter to check the voltage levels on the CAN bus wires. The CANH wire should typically be around 2.5V, and the CANL wire should be around 2.5V.
• Oscilloscope Testing: Use an oscilloscope to check the CAN bus signal for proper waveform and voltage levels.
• CAN Bus Analyzer: Use a CAN bus analyzer to monitor the traffic on the CAN bus and identify any errors or problems.

5. Advanced Techniques for Troubleshooting 51AE BMW Code

For complex cases, these techniques can help pinpoint the problem:

• Using BMW Diagnostic Tools (ISTA, etc.): BMW’s proprietary diagnostic tools offer in-depth analysis and guided troubleshooting steps.
• Checking Vehicle Communication (MOST) Bus: The Media Oriented Systems Transport (MOST) bus handles multimedia data. Interference can sometimes affect the CAN bus.
• Performing Voltage Drop Tests: This test identifies excessive resistance in the wiring, which can impede signal transmission.
• Analyzing Freeze Frame Data: This data, captured when the code was triggered, provides valuable clues about the conditions at the time of the fault.
• Reviewing BMW Service Bulletins: BMW releases service bulletins to address common issues. Reviewing these can provide insights into known problems and solutions.
• Data Logging: Record live data from various sensors and modules while driving to identify anomalies.

6. The Role of AutoExplain.com in Resolving BMW Electrical Issues

Navigating complex electrical issues like the 51AE code can be challenging. AutoExplain.com offers expert remote support to guide you through the diagnostic and repair process.

6.1 How AutoExplain.com Can Help

• Expert Technicians: Access experienced BMW technicians who specialize in electrical diagnostics.
• Remote Diagnostics: Get real-time assistance via WhatsApp, email, or other online platforms.
• Wiring Diagrams and Schematics: Obtain access to detailed wiring diagrams and schematics to help trace circuits and identify faults.
• Step-by-Step Guidance: Receive clear, step-by-step instructions on how to diagnose and repair the problem.
• Software Updates and Programming: Get assistance with ECU programming, coding, and software updates.
• Component Testing: Learn how to properly test components using a multimeter, oscilloscope, and other tools.
• CAN Bus Analysis: Get help analyzing CAN bus data to identify communication problems.

7. Why Choose AutoExplain.com?

• Expertise: Our team has extensive experience with BMW electrical systems.
• Efficiency: Remote support saves you time and money by avoiding unnecessary trips to the mechanic.
• Cost-Effectiveness: Get expert advice at a fraction of the cost of traditional repair shops.
• Convenience: Get help from the comfort of your own garage.
• Reliability: We provide accurate and reliable information to help you fix your car right the first time.

Alternative text: AutoExplain’s remote support team providing expert assistance for diagnosing and resolving complex automotive issues effectively and efficiently.

8. Common Questions about BMW Diagnostic Codes

Q1: What does it mean when my BMW throws a code?

A1: A diagnostic code means an electronic control unit (ECU) has detected a problem within a system. This could range from minor sensor issues to significant mechanical or electrical faults.

Q2: Can I diagnose BMW codes myself?

A2: Yes, with an OBD-II scanner, you can read the codes. However, interpreting them and performing accurate diagnostics often requires technical knowledge.

Q3: Are some BMW codes more serious than others?

A3: Absolutely. Codes related to safety systems (brakes, airbags) or critical engine functions are generally more urgent than those related to comfort features.

Q4: Will clearing the code fix the problem?

A4: Clearing the code only removes the symptom (the code itself). The underlying issue will persist and the code will likely return if not addressed.

Q5: How accurate are generic OBD-II scanners for BMWs?

A5: Generic scanners can read basic codes, but they may not provide the detailed information offered by BMW-specific diagnostic tools.

Q6: Where can I find reliable information about BMW codes?

A6: Reputable online forums, technical websites, and BMW service manuals are good sources. AutoExplain.com offers expert assistance and information as well.

Q7: What is the Controller Area Network (CAN) bus in a BMW?

A7: The CAN bus is a communication network that allows various electronic control units (ECUs) in the car to communicate with each other. It’s essential for modern automotive systems.

Q8: What is the MOST (Media Oriented Systems Transport) bus in a BMW?

A8: The Media Oriented Systems Transport (MOST) bus handles multimedia data. Interference can sometimes affect the CAN bus.

Q9: How does low voltage affect a BMW’s electronic systems?

A9: Low voltage can cause erratic behavior, trigger false codes, and even damage electronic components.

Q10: Why is it important to have a BMW-specific diagnostic tool?

A10: BMW-specific tools can access manufacturer-specific codes and perform advanced functions like coding, programming, and adaptation, which are crucial for many repairs.

9. How to Contact AutoExplain.com for Support

Don’t let the 51AE BMW code or any other electrical issue keep you off the road. Contact AutoExplain.com today for expert assistance:

• Address: 1500 N Grant ST Sten Denver, CO 80203
• WhatsApp: (+84)967469410
• Email: [email protected]
• Website: AutoExplain.com

Our team is ready to help you diagnose and repair your BMW quickly and efficiently. Get the expert support you need to get back on the road with confidence.