B1368

What Does Code B1368 Mean?

DTC B1368 signifies an “Ignition Tach Circuit Open” condition. This code indicates that the vehicle’s control module, typically the Body Control Module (BCM) or Powertrain Control Module (PCM), has detected an open circuit in the dedicated ignition tachometer signal pathway. The ignition tach circuit is responsible for providing an accurate engine RPM signal to various modules, most notably the instrument cluster’s tachometer, but also potentially to the BCM for starter interlock logic, the Transmission Control Module (TCM) for shift scheduling, or the PCM itself for cross-referencing engine speed data from other sensors. An “open” circuit means there is a discontinuity or break in the electrical path, preventing the proper voltage signal or pulse train from being transmitted or received. The module monitors this circuit for an expected pulse signal when the engine is running or cranking; if it detects a constant high or low voltage that does not correspond to engine operation, it interprets this as an open circuit and sets code B1368.

Common Symptoms

• Inoperative Tachometer: The most direct and common symptom, where the instrument cluster’s RPM gauge reads zero or is stuck.
• Malfunction Indicator Lamp (MIL) Illumination: The Check Engine Light or a specific system warning light may be activated.
• No-Start or Extended Crank: In some systems, the BCM or PCM may rely on this signal to confirm engine rotation for fuel pump activation or injector pulse, leading to a crank-no-start condition.
• Engine Stalling: Less common, but possible if critical modules lose engine speed input.
• Incorrect Automatic Transmission Shift Points: If the TCM utilizes this signal for precise shift scheduling, its absence or inaccuracy can lead to harsh or mistimed shifts.

What Causes the Code B1368?

• Open or Damaged Wiring: The most frequent cause, typically a broken, chafed, or corroded wire in the ignition tachometer signal circuit, often due to physical damage, heat exposure, or rodent activity.
• Poor or Corroded Electrical Connections: Loose, corroded, or spread terminals at multi-pin connectors along the signal path, including those at the ignition coil(s), ignition module, PCM/BCM, or instrument cluster.
• Faulty Instrument Cluster: An internal defect within the instrument cluster itself can create an open circuit at its tachometer input, preventing the signal from being processed.
• Faulty Ignition System Component: If the tach signal is derived directly from the primary side of an ignition coil or an integrated ignition control module, a fault in that component could stop the signal generation.
• Aftermarket System Interference: Improperly installed aftermarket alarm systems, remote start systems, or stereo equipment that tap into the ignition or tach signal wiring can create an open or short circuit.
• Faulty Body Control Module (BCM) or Powertrain Control Module (PCM): Less common, an internal failure within the control module responsible for monitoring or generating the tach signal can be the cause.

How to Diagnose and Troubleshoot

Diagnosing B1368 requires systematic electrical testing and careful examination of the ignition tachometer circuit. Always begin with the simplest checks and progress to more complex diagnostics.

1. Visual Inspection:
   • Begin with a thorough visual inspection of the entire ignition tachometer circuit, from its signal source (e.g., ignition coil primary, ignition module output, PCM output) to the destination (e.g., instrument cluster, BCM).
   • Look for obvious signs of physical damage to the wiring, such as chafing, cuts, melting, or corrosion. Pay close attention to areas where wiring passes through firewalls, over sharp edges, or near exhaust components.
   • Inspect all associated connectors for loose pins, corrosion, or contamination. Ensure connectors are fully seated.
   • Check all fuses related to the ignition system, instrument cluster, BCM, and PCM, as a blown fuse could de-power a relevant module or circuit.
2. OBD-II Scan Tool Data Analysis:
   • Connect an advanced OBD-II scan tool and retrieve all stored DTCs. Note any other codes present, as they may provide additional diagnostic direction.
   • Monitor live data parameters, specifically “Engine RPM” or “Tachometer Signal” if available. Start the engine (if possible) or crank it. Observe if the scan tool reports an RPM signal.
   • If the scan tool shows RPM while the instrument cluster tachometer is dead, the fault is likely downstream of the PCM’s ability to read the signal (e.g., wiring from PCM to cluster, or the cluster itself). If the scan tool also reports zero RPM, the fault is upstream of the PCM’s input or within the PCM’s processing.
3. Digital Multimeter (DMM) Testing:
   • Wiring Diagram Acquisition: Obtain the precise vehicle-specific wiring diagrams for the ignition tachometer circuit. These are crucial for identifying wire colors, pin locations, and splice points.
   • Continuity Test: Disconnect the relevant connectors (e.g., at the ignition source and destination module). Using a DMM set to continuity or resistance mode, test the tachometer signal wire. A reading of “OL” (Open Line) or very high resistance confirms a break in the circuit. Flex the wiring harness during this test to expose intermittent opens.
   • Voltage Test (Signal Output):
     • With the engine cranking or running (if it starts), backprobe the tachometer signal wire at its source (e.g., the negative side of the ignition coil, a dedicated tachometer output pin from an ignition module or PCM).
     • A DMM set to AC voltage or frequency mode (if available) should show a pulsating voltage signal (often a square wave or rapidly fluctuating DC voltage) that changes with engine speed.
     • If no signal is present at the source, the ignition component or control module generating the signal is likely faulty.
   • Voltage Drop Test: Perform a voltage drop test across connectors and wire sections in the tach circuit to identify high-resistance connections that might not be a complete open but can severely degrade the signal.
4. Component Isolation:
   • If the signal is present at the source but not reaching the destination module, systematically isolate sections of the wiring or components. For example, if the signal reaches the instrument cluster connector but the tachometer remains inoperative, the fault likely lies within the cluster itself.

Recommended Repairs and Solutions

Once the root cause of the B1368 code has been accurately identified through diagnosis, perform the following repairs:

• Repair or Replace Damaged Wiring: If an open circuit is found in the wiring harness, repair it using proper automotive wiring repair techniques (e.g., soldering, heat-shrink tubing). Avoid using crimp connectors for signal wires if possible. If the damage is extensive, replace the entire affected section of the wire or harness. Ensure proper strain relief for all repaired wires.
• Clean and Secure Connectors: If corrosion or loose terminals are found in the connectors, carefully clean the terminals using electrical contact cleaner and a small brush. Use a pick tool to carefully tighten spread terminals. Apply dielectric grease to prevent future corrosion and ensure a secure connection.
• Replace Faulty Components:
  • Instrument Cluster: If diagnostic steps confirm an internal fault with the instrument cluster’s tachometer circuit, replace the instrument cluster. Be aware that many modern instrument clusters require programming or calibration after replacement to function correctly and avoid additional DTCs or mileage discrepancies.
  • Ignition Coil/Module: If the primary signal source (e.g., an ignition coil with integrated tach output or a separate ignition control module) is determined to be faulty, replace the specific component.
  • BCM/PCM Replacement: This should be a last resort. If all other components and wiring have been thoroughly tested and verified as functional, and diagnostics strongly indicate an internal module failure, replace the BCM or PCM. Always remember that control module replacement often necessitates reprogramming or “flashing” with vehicle-specific software.
• Remove Aftermarket Devices: If an aftermarket alarm, remote start, or audio system is suspected of interfering with the circuit, temporarily disconnect it and re-test the tachometer circuit. If the issue resolves, either remove the aftermarket system or have it professionally re-wired to avoid circuit interference.

Mechanic’s Tips:
Always use OEM wiring diagrams; aftermarket diagrams may contain inaccuracies. When performing continuity or voltage tests on a circuit, gently manipulate the wiring harness, especially at common flex points and connector locations, to expose intermittent opens that might only appear under specific conditions. Pay close attention to ground circuits as a poor ground can often mimic an open circuit. After any repair, clear the DTCs with a scan tool and perform a road test or monitor live data to ensure the fault does not return and the system operates as intended.