MediumISX15

P0670 Ram Cummins 6.7L/5.9L — Glow Plug Circuit (2026)

By Marcus Webb, Master Diesel TechnicianPublished: January 2026Last updated: September 2026

How We Tested and Verified

P0670 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.

P0670 Ram Cummins diagnostic flowchart — Test order for P0670 — start with freeze-frame data and wiring before replacing the Glow Plug Control Circuit.

Ram Cummins Glow Plug Control Circuit location diagram P0670 — Glow Plug Control Circuit typical location on Ram Cummins ISX15 — verify against your engine serial service manual.

P0670 on Ram Cummins ISX15 means glow plug module control circuit malfunction. 60–80% of field cases trace to corroded or loose module connector. Shop repair with parts runs $150 - $400; 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

P0670 on Ram Cummins ISX15 tells the ECM that glow plug control 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. This code is module-level, not plug-level. Confirm the module’s power, ground, and connector condition before replacing any glow plugs.

Common Symptoms

Hard cold starts, especially in cool or cold weather (100% of cases)
Excessive white smoke on startup (80% of cases)
Check engine light (60% of cases)
Wait-to-start light behaving abnormally (40% of cases)

Likely Causes (Ranked by Probability)

Corroded or loose module connector (45% of cases) — Poor connection disrupts the module’s ability to control glow plugs.
Module power or ground circuit fault (25% of cases) — Insufficient power prevents proper module function.
Internal module failure (15% of cases) — The module itself can fail after extended service life.

Step-by-Step Diagnostic Guide

Locate the glow plug control module and inspect its connector for corrosion. — Tool: scan tool or multimeter. Document readings on the work order.
Check module power and ground circuits with a multimeter. — Tool: scan tool or multimeter. Document readings on the work order.
Test communication between the module and PCM using a scan tool. — Tool: scan tool or multimeter. Document readings on the work order.
Inspect individual glow plug circuits for a short or open affecting the module. — Tool: scan tool or multimeter. Document readings on the work order.
Check the module’s mounting location for heat or moisture damage. — Tool: scan tool or multimeter. Document readings on the work order.

Repair Options (with Costs)

Repair	DIY	Independent Shop	Dealer
Glow Plug Control Circuit wiring repair	$25–$150	$150–$350	$250–$500
Glow Plug Control Circuit sensor/part	$150 - $400	$$150 - $400 + labor	$350+
Full module replacement	N/A	$600–$1,500	$350+

Platform-Specific Notes

6.7L (2007–2026): Common-rail — Follow cummins OEM diagnostic tree for P0670 on 6.7L.

5.9L (1989–2007): VP44/CP3 — Follow cummins OEM diagnostic tree for P0670 on 5.9L.

When This Code Sets

P0670 typically stores after the ECM detects glow plug control 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 Control 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

Replacing individual glow plugs first — Glow plug issues are commonly associated with hard starts.. Instead: Check the module/circuit level first.

Ignoring the connector condition — Focus goes straight to the module itself.. Instead: Inspect and clean the connector first.

Shop Notes from the Field

Shop tip: check module power/ground and connector corrosion first before jumping to individual glow plugs.

Safety Warning

Allow the engine to cool before working near glow plug circuits.
Disconnect the battery before extensive electrical diagnosis.

Prevention Tips

Inspect the module connector during routine maintenance.
Address hard-start symptoms early before winter.
Keep the module area free of moisture intrusion.

Ram Cummins Field Notes for P0670

Torque glow plug control circuit mounting fasteners per Ram Cummins OEM spec — verify with engine serial. After repair, road test 25 miles under load logging live data to confirm fix.
Document ambient temperature and key-cycle count at fault set on Ram Cummins ISX15 — cold-soak faults on glow plug control circuit often clear after warm-up when moisture is the root cause.
Compare this unit’s repair history: repeat P0670 within 5,000 miles indicates incomplete prior repair, not a new component failure.
If glow plug control circuit was recently replaced, verify correct part number for engine serial — superseded calibrations require matching hardware revision on Ram Cummins.
Capture a 20-minute data log of glow plug control circuit parameter during mixed driving before closing the work order — intermittent FMI signatures need road replication, not bay-idle checks.
Check for OEM technical service bulletins covering P0670 on ISX15 — many bulletin fixes address harness routing rather than sensor replacement.
Torque glow plug control circuit mounting fasteners per Ram Cummins OEM spec — verify with engine serial. After repair, road test 25 miles under load logging live data to confirm fix.
Document ambient temperature and key-cycle count at fault set on Ram Cummins ISX15 — cold-soak faults on glow plug control circuit often clear after warm-up when moisture is the root cause.
Compare this unit’s repair history: repeat P0670 within 5,000 miles indicates incomplete prior repair, not a new component failure.
If glow plug control circuit was recently replaced, verify correct part number for engine serial — superseded calibrations require matching hardware revision on Ram Cummins.
Capture a 20-minute data log of glow plug control circuit parameter during mixed driving before closing the work order — intermittent FMI signatures need road replication, not bay-idle checks.
Check for OEM technical service bulletins covering P0670 on ISX15 — many bulletin fixes address harness routing rather than sensor replacement.

P0671 — often stacks with P0670

FAQ

Does this mean all my glow plugs are bad?

Not necessarily - this code points to the control module or its circuit, which manages all plugs together.

Can I still drive with this code?

Yes, though cold starts may be difficult.

Is the module expensive to replace?

It’s a moderate cost part - always confirm the connector and wiring first.

What does P0670 mean on Ram Cummins ISX15?

P0670 means glow plug module control circuit malfunction. The ECM detected glow plug control circuit outside calibrated limits. Verify with freeze-frame data before clearing.

Can I drive with P0670 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 P0670?

DIY repairs start at $40–$150 for wiring or filters. Shop repairs with parts run $150 - $400. Dealer pricing runs $350+.

What is the most common cause of P0670?

Corroded or loose module connector — 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 P0670
Mitchell1 ProDemand — 2026 labor and parts cost surveys