B0738 - N (neutral) Indicator Circuit High (BCM)

Introduction:

The B0738 diagnostic trouble code (DTC) indicates a problem within the Body Control Module (BCM) related to the neutral indicator circuit. Specifically, the BCM is detecting a higher-than-expected voltage in the circuit that signals whether the vehicle's transmission is in the neutral position. This can lead to various issues, from incorrect indicator lights to potential problems with systems relying on neutral gear status.

Table: B0738 - N (neutral) Indicator Circuit High (BCM) - Comprehensive Information

Aspect	Description	Possible Causes
Definition	N (Neutral) Indicator Circuit High (BCM) - indicates the Body Control Module (BCM) is detecting a voltage exceeding the expected range on the neutral indicator circuit.	Short to voltage in the neutral indicator circuit wiring, Faulty neutral safety switch (NSS), Internal BCM failure, Corroded or damaged connectors in the circuit, Wiring harness damage (chafing, breaks), Incorrectly adjusted NSS.
Symptoms	Neutral indicator light illuminated when not in neutral, Neutral indicator light not illuminating when in neutral, Vehicle not starting in park or neutral, Erratic shifting, Cruise control malfunction, Remote start inoperative, Other BCM-related issues.	BCM misinterpreting gear position, System relying on neutral status failing, Safety features compromised.
Possible Causes (Detailed)
Short to Voltage	A wire in the neutral indicator circuit is making unintended contact with a voltage source.	Damaged wiring insulation, Improperly routed wiring, Aftermarket electrical modifications.
Faulty NSS	The Neutral Safety Switch (also called Transmission Range Sensor or Park/Neutral Position Switch) is malfunctioning and sending an incorrect signal to the BCM.	Physical damage to the switch, Corrosion, Wear and tear, Misadjustment.
Internal BCM Failure	The BCM itself has an internal electronic fault affecting its ability to correctly interpret the neutral indicator signal.	Internal component failure, Water damage, Electrical surges.
Corroded Connectors	Corrosion on connectors within the neutral indicator circuit is increasing resistance and affecting voltage readings.	Exposure to moisture, Salt, Road debris.
Wiring Harness Damage	Damage to the wiring harness, such as chafing or breaks, is causing a short to voltage or an open circuit.	Rubbing against sharp edges, Rodent damage, Heat exposure.
NSS Misadjustment	The NSS is not properly aligned or adjusted, causing it to send an incorrect signal to the BCM.	Improper installation, Loosened mounting hardware, Physical impact.
Diagnostic Steps	Connect a scan tool to the vehicle's OBD-II port, Read and record all DTCs, including pending codes, Inspect the neutral safety switch and its wiring, Check the wiring harness for damage, Test the neutral indicator circuit for shorts to voltage, Test the neutral safety switch for proper operation, Test the BCM inputs and outputs, Consult the vehicle's service manual for specific diagnostic procedures.	Accurate identification of the root cause, Avoiding unnecessary repairs.
Tools Required	OBD-II scan tool, Multimeter, Wiring diagram, Test light, Basic hand tools.	Accurate diagnosis and repair.
Related Codes	B0737 (N Neutral Indicator Circuit Low), P0705 (Transmission Range Sensor Circuit Malfunction), P0706 (Transmission Range Sensor Circuit Range/Performance), P0707 (Transmission Range Sensor Circuit Low Input), P0708 (Transmission Range Sensor Circuit High Input).	These codes can provide additional information about the nature of the problem.
Severity	Moderate to High - Can prevent the vehicle from starting, affect shifting, and compromise safety features.	Potential for vehicle malfunction and safety risks.
Repair Costs	Varies widely depending on the cause - from a simple wiring repair to replacing the BCM. Labor rates and parts prices will affect the final cost.	Accurate cost assessment.

Detailed Explanations:

Definition: The B0738 code specifically means the Body Control Module (BCM) is detecting a higher than expected voltage on the neutral indicator circuit. This circuit is designed to inform the BCM when the transmission is in neutral, and the BCM uses this information for various functions.

Symptoms: A common symptom is the neutral indicator light illuminating when the vehicle is not in neutral, or not illuminating when it is in neutral. The vehicle might not start in park or neutral, and you may experience erratic shifting, cruise control malfunctions, or remote start failures. These issues stem from the BCM misinterpreting the gear position.

Possible Causes (Detailed):

Short to Voltage: This happens when a wire in the neutral indicator circuit comes into contact with a voltage source it shouldn't be touching. This can be due to damaged insulation exposing the wire, improper wiring routing causing contact, or aftermarket electrical modifications that weren't properly installed.
Faulty NSS: The Neutral Safety Switch (NSS), sometimes called the Transmission Range Sensor or Park/Neutral Position Switch, is responsible for telling the BCM what gear the transmission is in. If the NSS is malfunctioning, it can send an incorrect signal, leading to the B0738 code. This can be due to physical damage, corrosion, wear and tear, or misadjustment.
Internal BCM Failure: In rare cases, the BCM itself might have an internal electronic fault that affects its ability to correctly interpret the neutral indicator signal. This can result from internal component failure, water damage, or electrical surges.
Corroded Connectors: Corrosion on the connectors within the neutral indicator circuit can increase resistance and affect voltage readings. This is especially common in areas exposed to moisture, salt, and road debris.
Wiring Harness Damage: Damage to the wiring harness, such as chafing or breaks, can cause a short to voltage or an open circuit. Look for areas where the harness might rub against sharp edges or where rodents might have chewed on the wires.
NSS Misadjustment: If the NSS is not properly aligned or adjusted, it can send an incorrect signal to the BCM. This can happen after an improper installation, if the mounting hardware has loosened, or if the switch has sustained physical impact.

Diagnostic Steps:

Connect a scan tool: Use an OBD-II scan tool to read and record all DTCs, including pending codes. This provides valuable information about the problem.
Inspect the NSS: Visually inspect the neutral safety switch and its wiring for any signs of damage or corrosion.
Check the wiring harness: Carefully examine the wiring harness for damage, such as chafing or breaks.
Test for shorts to voltage: Use a multimeter to test the neutral indicator circuit for shorts to voltage.
Test the NSS: Use a multimeter to test the neutral safety switch for proper operation. Follow the vehicle's service manual for specific testing procedures.
Test BCM inputs and outputs: Test the BCM inputs and outputs related to the neutral indicator circuit to verify its functionality.
Consult the service manual: Always consult the vehicle's service manual for specific diagnostic procedures and wiring diagrams.

Tools Required:

OBD-II Scan Tool: To read and clear diagnostic trouble codes.
Multimeter: To test voltage, continuity, and resistance in the circuit.
Wiring Diagram: To understand the circuit layout and identify components.
Test Light: To quickly check for power and ground.
Basic Hand Tools: Such as wrenches, sockets, and screwdrivers.

Related Codes:

B0737 (N Neutral Indicator Circuit Low): Indicates a lower-than-expected voltage in the neutral indicator circuit.
P0705 (Transmission Range Sensor Circuit Malfunction): General code indicating a problem with the transmission range sensor circuit.
P0706 (Transmission Range Sensor Circuit Range/Performance): Indicates the transmission range sensor signal is out of range.
P0707 (Transmission Range Sensor Circuit Low Input): Indicates a low input signal from the transmission range sensor.
P0708 (Transmission Range Sensor Circuit High Input): Indicates a high input signal from the transmission range sensor.

These related codes can help narrow down the specific cause of the B0738 code.

Severity: The severity of the B0738 code can range from moderate to high. It can prevent the vehicle from starting, affect shifting, and compromise safety features like cruise control and remote start.

Repair Costs: Repair costs can vary widely depending on the underlying cause. A simple wiring repair might cost a few hundred dollars, while replacing the BCM could cost significantly more. Labor rates and parts prices will also affect the final cost. Getting a proper diagnosis from a qualified mechanic is crucial for accurate cost estimation.

Frequently Asked Questions:

What does the B0738 code mean? It means the Body Control Module (BCM) is detecting a higher-than-expected voltage in the neutral indicator circuit.
Can I drive my car with a B0738 code? It's not recommended, as it could affect shifting and starting, potentially leading to safety issues.
Is the B0738 code serious? Yes, it can prevent the vehicle from starting and affect safety features.
Can I fix the B0738 code myself? If you have experience with automotive electrical systems and access to the necessary tools, you might be able to diagnose and repair the issue. However, it's often best left to a qualified mechanic.
How do I clear the B0738 code? Use an OBD-II scan tool to clear the code after the problem has been fixed. Note that the code may return if the underlying issue is not resolved.

Conclusion:

The B0738 code indicates a problem with the neutral indicator circuit, specifically a high voltage reading being detected by the BCM. Thorough diagnosis involving checking wiring, the neutral safety switch, and the BCM itself is essential to resolve the issue and ensure vehicle safety and functionality.