P0615 -- Starter Relay Circuit Malfunction Powertrain OBD-II

P0615 - Starter Relay Circuit Malfunction (Powertrain OBD-II)

Overview

• What it is: P0615 is a powertrain OBD-II code tied to the starter relay circuit. The open-source code reference title Circuito do relé de partida identifies this area as the starter relay circuit (starter relay control/energizing path). This supports the expectation that the PCM/ECM controls a starter relay and a fault in that circuit can throw P0615.
• Where it sits in OBD-II: P0615 is a powertrain (P) code, i.e., part of the engine/transmission control systems monitored by the OBD-II port and PCM. This aligns with the general description of DTCs and powertrain codes in the OBD-II references.
• Additional context: OBD-II systems monitor various parameters and generate DTCs when issues are detected (section on Diagnostic Trouble Codes, Powertrain Codes). Emissions-related readiness and monitoring are also described in OBD-II reference material.

Symptoms (typical user-reported complaints)

• Vehicle fails to crank or start when the key is turned or the start button is pressed.
• Starter may click, or you hear a single or multiple relay-like clicks but the engine does not crank.
• Engine may crank intermittently but fail to start, or starts inconsistently.
• In some cases, the starter may energize momentarily and then stop, with DTC P0615 stored or pending.
• Symptoms can coincide with low battery conditions or electronic control issues, but P0615 specifically points to the starter relay circuit.

Important Notes

• P0615 points to the relay control side (PCM/vehicle control signal to the relay coil) and/or the relay itself, not necessarily the physical starter motor. However, a faulty starter motor can mimic a relay problem, so confirm the actual culprit with proper testing.

What This Code Means

• Code meaning alignment: The confirmed open-source entry indicates the code is connected to the starter relay circuit, consistent with P0615 being a starter relay circuit issue. This aligns with standard code naming conventions in OBD-II "P" codes (Powertrain). See the GitHub definition reference for the code theme, and Wikipedia's OBD-II sections for general DTC/powertrain code context.

Diagnostic Approach

1) Verify the fault and scope

• Use the scan tool to confirm P0615 is present and to pull any freeze-frame data and pending vs stored status.
• Check for additional P-codes or U-codes that might indicate related issues (e.g., ignition, crank sensor, power supply faults) that could lead to a relay circuit fault.
• Confirm symptoms are reproducible or intermittent; intermittent faults require different diagnostic emphasis than a solid no-start.

2) Visual and readiness checks

• Battery condition: test resting voltage (should be near 12.6 V with engine off) and charging voltage (typically 13.8-14.8 V with engine running). Low voltage can prevent relay coil energizing.
• Battery terminals and grounds: inspect for corrosion, looseness, and proper torque on battery posts and main ground strap to the chassis and engine block.
• Starter relay and fuse box: inspect the starter relay(s) and associated fuses for signs of overheating, corrosion, or damage. Swap or test the relay with a known-good relay if feasible.
• Wiring harness: inspect the relay control circuit wiring from the ignition switch/PCM to the relay coil for damage, chafing, or loose connections. Look for signs of aftermarket wiring or bodged repairs.

3) Relay function test

• Relay swap test: If there is a known-good relay of the same type, swap it into the starter relay position. If the problem follows the relay, the relay is faulty.
• Coil circuit test: With appropriate safety measures (engine off, keys removed), measure coil resistance of the relay according to OEM/spec values. Compare to spec; a coil that is open or out of range indicates a faulty relay.
• Relay operation test: With the engine off, energize the relay coil (12 V) and listen for a distinct click indicating the relay is engaging. Then verify continuity between the input and output contacts when energized.

4) Electrical control signal verification (PCM/ignition switch)

• Confirm that the PCM/ECM is actually energizing the relay coil when starting:
  • Back-probe the relay coil control circuit (the side that receives 12 V when starting) and monitor for 12 V when the key is in START or the start signal is active.
  • Check the ground on the relay coil circuit; ensure a solid ground path when the relay is commanded.
• Inspect the ignition switch/Start signal path: a faulty ignition switch or a defective signal path can prevent the PCM from sending the start signal to the relay.

5) Crank/engine sensing and related inputs

• If the PCM isn't issuing a start command (even with a proper relay and wiring), verify crank-related inputs are present or correctly sensed (e.g., crankshaft position sensor signals, engine speed data). Faulty crank input can cause the PCM to fail to energize the starter relay.
• Look for immobilizer/anti-theft interactions that may prevent the PCM from commanding the starter relay.

6) Grounds and power integrity

• Check essential engine grounds and chassis grounds. A weak or corroded ground can cause relay coil or PCM control issues.
• Inspect power supply to the PCM and relay driver circuits for any voltage drops or interrupt conditions, especially under cranking load.

7) Mechanical starter-related checks

• Although P0615 targets the relay circuit, a failing starter solenoid or a seized starter can present symptoms similar to an intermittent relay issue. If relay tests are OK but the engine still won't crank, test the starter motor operation or bench-test with a known-good supply to confirm mechanical function.
• If a starter replacement is required, verify electrical connections after installation and recheck DTCs.

8) Post-repair verification

• After any fix (relay replacement, wiring repair, battery/ground improvements, starter replacement), clear the DTCs and perform a cranking/start test to confirm the issue is resolved.
• Re-scan to ensure no new DTCs are stored and that P0615 does not return.
• Confirm test drives show no intermittent start issues and verify no related circuits produce faults under real-world operation.

Probable Causes

Note: do not contain quantified NHTSA complaint frequencies for P0615. The following probabilities are approximate, experience-based estimates to help guide prioritization.

• Faulty starter relay (or relay coil failure) - ~40-50%: Most common cause when P0615 points to the relay circuit.
• Faulty or degraded PCM control signal to relay; ignition/start switch issues or wiring faults in the control path - ~20-30%: PCM output or control path failures commonly present as relay circuit faults.
• Battery/charging issues or poor connections (low voltage to relay coil, weak ground) - ~15-25%: Insufficient voltage often prevents the relay from energizing reliably.
• Wiring harness damage, corrosion, or poor ground connections in the relay circuit - ~5-10%: Electrical corrosion or damaged wires can disrupt the circuit.
• Faulty starter motor or seized starter (less common for a P0615-only symptom, but possible if the relay energizes intermittently or the mechanical path is blocked) - ~5-10%: Typically not the primary P0615 cause but must be checked if relay tests are inconclusive.
• Faulty PCM/ECM sensing inputs or immobilizer-related control faults - ~5-10%: Less common, but can manifest as inability to energize the relay due to perceived no-start condition.

Safety Considerations

• Disconnect the battery when performing mechanical work on the relay, wiring, or starter to avoid short circuits or arcing.
• If testing high-current circuits (starter and main power paths), use insulated tools and proper PPE. Be mindful of stored energy in the starter and battery.
• Never energize or bench-test live high-current circuits with exposed contacts; perform tests with appropriate protection and in a controlled environment.

Tools and data you may need

• Multimeter (for voltage checks, continuity, and coil resistance)

• Relay tester or known-good relay of the same type

• Scan tool with ability to read freeze-frame data, readiness status, and live data PIDs

• Basic hand tools (screwdrivers, pliers, Torx/Hex bits as needed for relay box access)

• OEM wiring diagrams or service information to confirm the correct control and power paths for the starter relay

• OBD-II overview and DTC concepts: Wikipedia, OBD-II - Diagnostic Trouble Codes; OBD-II - Powertrain Codes; OBD-II - Emissions Testing sections. These sections describe how modern systems monitor parameters and generate DTCs, and how powertrain codes are categorized in OBD-II. This provides the framework for understanding P0615 as a powertrain (P) code and its relation to engine/starting/relay circuitry.

• Code definition and scope (starter relay): Open-source entry titled Circuito do relé de partida, which indicates this code relates to the starter relay circuit. This aligns with the interpretation of P0615 as a starter relay circuit issue and provides a reference point for what the circuit entails.

• Emissions and readiness context: While not diagnostic steps themselves, the OBD-II Emissions Testing section notes that readiness monitors may be involved in how and when codes are cleared or re-tested, which can be relevant if the vehicle's readiness monitors are affected by a starter-related fault.

What to do next

• If you're diagnosing a vehicle with P0615:
  • Start with the simplest, high-probability checks: battery health, terminal cleanliness, ground paths, and the starter relay condition.
  • Progress to testing the relay coil control circuit from the PCM/ignition switch (voltage presence at the relay coil when starting, proper ground, and no excessive voltage drop).
  • Swap in a known-good relay to quickly determine if the relay is the root cause.
  • If the relay and wiring check out, test the starter motor itself for mechanical and electrical faults, including solenoid operation and current draw under cranking.
  • After repairs, clear codes and perform a thorough start test under load to confirm resolution. Re-scan to verify no new codes appear.

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II
• Open-Source OBD2 Data: N/A (MIT)

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

---