OBD-II Diagnostic Trouble Code
P1693 — Glow Plug Control Module Communication Lost
P1693 is a manufacturer-specific code that commonly means the ECM lost communication with the glow plug control module. Without data from it, the ECM cannot control or monitor glow plugs. Meaning can vary by OEM.
Severity 3/5
Truck-relevant
Service this week
Severity
Service this week
Glow Plug Control Module Communication Lost
Code
P1693
Category
Powertrain
Subsystem
Cold Start
Truck-relevant
Yes
What this means for truckers
P1693 (Glow Plug Control Module Communication Lost) — cold-start performance degraded. The GPCM can't talk to the ECM. Trucks with this code will have hard cold starts in freezing weather. Fix: GPCM is typically near the firewall on commercial diesels. Check connector + wiring first. GPCM replacement: $250-700.
Before you replace parts — try this first
P1693 on the Cold Start system is most often faulty communication wiring or connector — 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
Hard cold starts, white smoke on start-up, wait-to-start light issues, and a check-engine light.
Common causes
- CommonFaulty communication wiring or connector ($100–$400)
- CommonLoss of power or ground to the glow plug module ($80–$300)
- OccasionalFailed glow plug control module ($250–$700)
- RareECM fault ($800–$2500)
How to fix
Check the module fuse, power and ground
When to use: First step
Inspect the communication wiring
When to use: When power is good
Replace the glow plug module
When to use: When the module does not respond
Diagnose the ECM
When to use: When the module and wiring are good
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
- → P1607 — Internal Control Module Performance
- → P1635 — 5 Volt Reference 1 Circuit
- → P1638 — 5 Volt Reference 2 Circuit
- → P1654 — AC Refrigerant Pressure Switch Performance
- → P1690 — Wastegate Control Boost Pressure Out of Range
Frequently Asked Questions
Can I drive with code P1693?
P1693 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 P1693 on a commercial truck?
Total repair cost ranges $80–$2500 depending on the root cause. The cheapest fix is usually the first one listed below — Faulty communication wiring or connector — 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 P1693 fail a DOT inspection?
P1693 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 P1693 and related codes?
P1693 is closely related to: P1607 (Internal Control Module Performance), P1635 (5 Volt Reference 1 Circuit), P1638 (5 Volt Reference 2 Circuit), P1654 (AC Refrigerant Pressure Switch Performance). These codes share the same subsystem (cold-start) 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 P1693 is set without the companions, the issue is more isolated.
How do I prevent P1693 from coming back after a repair?
For P1693 (Glow Plug Control Module Communication Lost), prevention centers on the cold start system. Test glow plug system annually before winter. Use a battery in good condition — weak batteries make glow plugs work harder. Park indoors below -10°F if possible.