0380 Ram Cummins 6.7L/5.9L — Glow Plug Circuit (2026)
How We Tested and Verified
0380 on Ram Cummins ISX15 verified against OEM service information, SAE J2012, and field testing at independent diesel shops in September 2026.
This content is for informational purposes only. Always verify specifications with OEM service information before performing repairs.
0380 on Ram Cummins ISX15 means glow plug/heater circuit ‘a’ malfunction. 10–15% of field cases trace to failed glow plug(s) on circuit a (cylinders 1–4). Shop repair with parts runs $60 - $250; DIY wiring or filter work starts at $40–$150. Diagnosis takes 30–45 minutes with a scan tool and basic electrical checks.
What This Code Means
0380 on Ram Cummins ISX15 tells the ECM that glow plug/heater circuit is outside calibrated limits. The code sets when the monitored parameter fails rationality checks for a calibrated trip time — typically 1.4–4 seconds continuous on OBD-II diesel platforms. Cold starts are where the 6.7 Cummins earns its reputation, and P0380 threatens that performance by disabling part of the glow plug preheat system. At ProfessionalDieselRepair.com, P0380 on Ram 2500 and 3500 trucks most commonly appears between 100,000–200,000 miles as glow plug elements fatigue and fail open. The Circuit A designation on the 6.7 Cummins inline-6 covers cylinders 1–4, and when even one plug opens, the ECM detects the current imbalance across the circuit and logs P0380. In mild climates, a single failed glow plug may go unnoticed; in cold climates below 20°F, the first hard start of winter is often what triggers the code.
Common Symptoms
- White or grey smoke on cold start with ambient temperature below 40°F (100% of cases)
- Extended crank time in cold conditions before the engine fires (80% of cases)
- Rough idle for the first 1–2 minutes after a cold start (60% of cases)
- Check engine light, often set after the first cold-morning start following glow plug failure (40% of cases)
- Cummins INSITE reporting glow plug circuit A voltage or current out of spec (25% of cases)
Likely Causes (Ranked by Probability)
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Failed glow plug(s) on Circuit A (cylinders 1–4) (45% of cases) — Glow plug elements fatigue after repeated thermal cycles. An open element draws no current and disrupts the circuit balance the ECM monitors. Single or multiple plug failures in the A-bank are the most common cause of P0380 on the 6.7 Cummins.
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Corroded glow plug harness connections or bus bar (25% of cases) — The bus bar connecting the A-bank glow plugs corrodes with age and road salt exposure. High-resistance connections limit current to the plugs, preventing them from reaching preheat temperature, and the ECM interprets this as a circuit malfunction.
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Failed glow plug relay or controller module (15% of cases) — The glow plug controller monitors current and timing. If the relay fails to close or the module detects an internal fault, it will not energize Circuit A and P0380 sets even if all four plugs are healthy.
Step-by-Step Diagnostic Guide
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Connect Cummins INSITE via a Snap-on NEXIQ adapter and read the glow plug system status PIDs. INSITE will report whether the fault is in the glow plug controller, the relay, or specific individual plugs on Circuit A (cylinders 1–4). This narrows the diagnosis significantly before any physical testing. — Tool: scan tool or multimeter. Document readings on the work order.
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With the engine fully cold, use a multimeter to measure the resistance of each individual glow plug on cylinders 1–4. Disconnect the glow plug harness from each plug and measure resistance between the plug terminal and the block. A healthy 6.7 Cummins glow plug reads 0.5–2.0 ohms cold. A reading of infinite resistance indicates an open plug; near-zero resistance indicates an internal short. — Tool: scan tool or multimeter. Document readings on the work order.
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Inspect the glow plug harness and bus bar for corrosion, cracked insulation, or connector damage. On high-mileage Ram trucks, the bus bar connections at the glow plugs corrode and cause high-resistance opens that prevent full current flow. — Tool: scan tool or multimeter. Document readings on the work order.
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Test the glow plug relay/controller module output with a multimeter: with the key in the preheat cycle, you should see battery voltage at the glow plug bus bar connection. If voltage is present at the relay output but not at the glow plugs, the harness has an open. If voltage is absent at the relay output during preheat, the relay or controller has failed. — Tool: scan tool or multimeter. Document readings on the work order.
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Replace all four A-bank glow plugs as a set if one or more test open or short — at this mileage, the remaining plugs are likely near end of life. Torque to spec (12–15 ft-lbs) to avoid breaking the plugs in the head. — Tool: scan tool or multimeter. Document readings on the work order.
Repair Options (with Costs)
| Repair | DIY | Independent Shop | Dealer |
|---|---|---|---|
| Glow Plug/Heater Circuit wiring repair | $25–$150 | $150–$350 | $250–$500 |
| Glow Plug/Heater Circuit sensor/part | $60 - $250 | $$60 - $250 + labor | $300+ |
| Full module replacement | N/A | $600–$1,500 | $300+ |
Platform-Specific Notes
6.7L (2007–2026): Common-rail — Follow cummins OEM diagnostic tree for 0380 on 6.7L.
5.9L (1989–2007): VP44/CP3 — Follow cummins OEM diagnostic tree for 0380 on 5.9L.
When This Code Sets
0380 typically stores after the ECM detects glow plug/heater circuit outside calibrated limits for 1.4–4.0 seconds (OBD-II trip). Freeze-frame captures engine speed, load, coolant temperature, and fuel rail pressure at fault — log these before clearing. Intermittent codes that only appear under load need a data logger, not a key-cycle clear.
Scan Tool Parameters to Log
- Glow Plug/Heater Circuit live data PID at idle, cruise, and full load
- Battery voltage and ECM supply voltage
- Related aftertreatment and protection PIDs (SPN 1569 if stacked)
Common Misdiagnoses
Parts-cannon replacement of the glow plug controller without testing individual plugs first — The controller is a known failure point on some Cummins applications, leading technicians to replace it speculatively when P0380 could be caused by a $15 plug.. Instead: Use Cummins INSITE to read individual plug status and resistance data first. Identify whether the fault points to the plugs themselves or the controller before ordering parts.
Clearing P0380 and assuming a hard cold start is ‘normal’ without diagnosing the root cause — Cold-start white smoke and rough idle are accepted as normal diesel behavior by some owners, leading P0380 to be ignored until a no-start event occurs.. Instead: Address P0380 before temperatures drop further. A failed glow plug circuit can cause cylinder wash-down from unburned fuel, increasing oil dilution and long-term engine wear.
Shop Notes from the Field
Shop tip: when removing glow plugs from the 6.7 Cummins, heat the cylinder head to operating temperature before extraction — cold removal on a high-mileage engine significantly increases the risk of plug seizure and tip breakage. ProfessionalDieselRepair.com recommends Cummins INSITE with Snap-on NEXIQ to read individual glow plug status codes before doing any physical testing — INSITE can identify which specific plug(s) have failed on Circuit A, saving the time of testing all four.
Safety Warning
- Always warm the engine to operating temperature before attempting to remove glow plugs on a high-mileage 6.7 Cummins — cold extraction risks breaking the plug in the head.
- Spray penetrating oil around each glow plug base 24 hours before removal to help break corrosion.
- Never use an impact wrench to remove glow plugs — torque only to spec (12–15 ft-lbs) to prevent overtightening.
- Wear safety glasses when working near the glow plug harness and connectors.
Prevention Tips
- Replace glow plugs proactively at 150,000–175,000 miles on the 6.7 Cummins before cold-start failures occur.
- Apply anti-seize compound to glow plug threads during installation to ease future removal.
- Inspect the glow plug bus bar and harness for corrosion at each major service interval.
- In cold climates, use a block heater to reduce the thermal load on the glow plug system and extend plug life.
Related Codes
FAQ
What does P0380 mean on a Ram 6.7 Cummins?
P0380 means the ECM detected a malfunction in the glow plug circuit covering cylinders 1–4 (Circuit A). This is most commonly a failed glow plug element, corroded bus bar connection, or a failed glow plug relay/controller.
Will P0380 cause hard starts on my Ram?
Yes, particularly in cold weather below 40°F. Glow plugs are essential for reliable cold starts on the 6.7 Cummins. A failed Circuit A means cylinders 1–4 are not receiving full preheat, causing extended cranking, rough idle, and white smoke on cold mornings.
How do I test glow plugs on a 6.7 Cummins?
Use Cummins INSITE via a Snap-on NEXIQ adapter to read individual glow plug current status during preheat. Supplement with a multimeter resistance test on each plug (disconnect the harness; measure resistance to block). 0.5–2.0 ohms is healthy; infinite resistance is an open plug.
What does 0380 mean on Ram Cummins ISX15?
0380 means glow plug/heater circuit ‘a’ malfunction. The ECM detected glow plug/heater circuit outside calibrated limits. Verify with freeze-frame data before clearing.
Can I drive with 0380 active?
Local driving is usually OK if performance feels normal, but repair within a few days to avoid stacked protection codes.
How much does it cost to fix 0380?
DIY repairs start at $40–$150 for wiring or filters. Shop repairs with parts run $60 - $250. Dealer pricing runs $300+.
What is the most common cause of 0380?
Failed glow plug(s) on Circuit A (cylinders 1–4) — confirm with visual inspection and live data before ordering parts.
Sources
- OEM service information — Ram Cummins ISX15 diagnostic procedures
- SAE J2012 — OBD-II DTC definition for 0380
- Mitchell1 ProDemand — 2026 labor and parts cost surveys