OBD-II Diagnostic Trouble Code
P0740 — Torque Converter Clutch Circuit Malfunction
P0740 indicates a malfunction in the torque converter clutch (TCC) control circuit. The TCM saw an electrical or operational fault in the solenoid circuit that applies the converter lockup clutch.
Severity 3/5
Truck-relevant
Service this week
Severity
Service this week
Torque Converter Clutch Circuit Malfunction
Code
P0740
Category
Powertrain
Subsystem
Transmission
Truck-relevant
Yes
What this means for truckers
Service within a few days on a Cummins X15, Detroit DD15, PACCAR MX-13. Performance is likely degraded. Continuing to drive without service risks additional component damage.
Before you replace parts — try this first
P0740 on the Transmission system is most often failed tcc solenoid — 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 converter lockup causing higher cruise RPM, poor fuel economy and transmission overheating, or shudder; check-engine light.
Common causes
- CommonFailed TCC solenoid ($250–$800)
- CommonDamaged wiring or connector ($100–$450)
- OccasionalLow or contaminated fluid ($100–$600)
- OccasionalWorn torque converter clutch ($2000–$5000)
How to fix
Check fluid
When to use: First
Measure TCC solenoid resistance and circuit integrity
When to use: When fluid is good
Command TCC on with a scan tool and watch slip speed
When to use: To separate a mechanical fault from an electrical one
Replace the torque converter
When to use: When slip persists with a good solenoid and circuit
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
- → P0700 — Transmission Control System Malfunction
- → P0701 — Transmission Control System Range/Performance
- → P0702 — Transmission Control System Electrical
- → P0703 — Brake Switch B Circuit
- → P0705 — Transmission Range Sensor Circuit Malfunction
Frequently Asked Questions
Can I drive with code P0740?
P0740 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 P0740 on a commercial truck?
Total repair cost ranges $100–$5000 depending on the root cause. The cheapest fix is usually the first one listed below — Failed TCC solenoid — 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 P0740 fail a DOT inspection?
P0740 typically doesn't fail an inspection on its own. Inspectors focus on safety items (brakes, steering, tires, lights, HOS). Transmission codes only become an issue if the truck has shifting problems severe enough to qualify as 'mechanical fitness' OOS. Fix to prevent escalation.
What's the difference between P0740 and related codes?
P0740 is closely related to: P0700 (Transmission Control System Malfunction), P0701 (Transmission Control System Range/Performance), P0702 (Transmission Control System Electrical), P0703 (Brake Switch B Circuit). These codes share the same subsystem (transmission) 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 P0740 is set without the companions, the issue is more isolated.
How do I prevent P0740 from coming back after a repair?
For P0740 (Torque Converter Clutch Circuit Malfunction), prevention centers on the transmission system. Service transmission fluid at the OEM interval (typically 150K–250K miles for HD autos). Don't skip the magnet/strainer inspection. After repair, perform an adaptive shift relearn with a scan tool (or drive 40+ miles for adaptive ECMs to relearn naturally).