OBD-II Diagnostic Trouble Code
P0615 — Starter Relay Circuit
P0615 means the ECM detected a general fault in the starter relay control circuit. The commanded state doesn't match what the ECM reads back on the circuit, which points to an open, a short, or a bad relay. It's mostly used on vehicles where the ECM controls the starter relay.
Severity 3/5
Truck-relevant
Service this week
Severity
Service this week
Starter Relay Circuit
Code
P0615
Category
Powertrain
Subsystem
Ignition
Truck-relevant
Yes
What this means for truckers
P0615 (Starter Relay Circuit) — starter relay circuit fault.
Before you replace parts — try this first
P0615 on the Ignition system is most often failed starter relay — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
No-crank, intermittent no-crank, or in some cases a starter that keeps running or won't disengage. The check-engine light may come on. Turning the key or pressing start may only produce a click.
Common causes
- CommonFailed starter relay ($40–$200)
- OccasionalOpen or high-resistance starter relay control wire ($120–$400)
- OccasionalCorroded relay socket or connector ($60–$250)
- OccasionalNeutral safety or clutch switch input problem affecting starter enable ($80–$400)
- RareFailed ECM starter relay driver ($1200–$3500)
How to fix
Swap the starter relay with a known-good one
When to use: First, quick test
Use a test light to check for the relay control signal and ground during crank
When to use: When swapping the relay doesn't fix it
Check the starter-enable inputs (neutral or clutch switch) on a scan tool
When to use: When the ECM isn't commanding the relay
Repair the control wiring, or replace the ECM if the driver has failed
When to use: After you've isolated the circuit fault
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
- → Browse all DTC trouble codes
- → Decode a VIN to check codes for your truck
- → Owner-operator maintenance guides
- → P0670 — Glow Plug Control Module Circuit
- → P0671 — Cylinder 1 Glow Plug Circuit
- → P0672 — Cylinder 2 Glow Plug Circuit
- → P0673 — Cylinder 3 Glow Plug Circuit
- → P0674 — Cylinder 4 Glow Plug Circuit
Frequently Asked Questions
Can I drive with code P0615?
P0615 is severity 3 — plan service within a few days. Performance is likely degraded already (you may feel reduced power, harsher shifts, or slightly worse fuel economy). Continuing to drive risks additional damage to adjacent components.
How much does it cost to fix P0615 on a commercial truck?
Total repair cost ranges $40–$3500 depending on the root cause. The cheapest fix is usually the first one listed below — Failed starter relay — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will P0615 fail a DOT inspection?
P0615 is generally not a direct DOT inspection fail item by itself. Inspectors focus on safety-critical systems (brakes, steering, tires, lights, hours-of-service). However, the check engine light alone can trigger additional inspection scrutiny. Best practice: fix the code and clear it before a planned inspection.
What's the difference between P0615 and related codes?
P0615 is closely related to: P0670 (Glow Plug Control Module Circuit), P0671 (Cylinder 1 Glow Plug Circuit), P0672 (Cylinder 2 Glow Plug Circuit), P0673 (Cylinder 3 Glow Plug Circuit). These codes share the same subsystem (ignition) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only P0615 is set without the companions, the issue is more isolated.
How do I prevent P0615 from coming back after a repair?
For P0615 (Starter Relay Circuit), prevention centers on the ignition system. Use OEM-spec injectors and spark plugs (gas). Address fuel quality issues immediately — bad fuel kills injectors. Cylinder balance test annually for early warning.