OBD-II Diagnostic Trouble Code
P1742 — Torque Converter Clutch Solenoid Failed
P1742 is a manufacturer-specific code that commonly means the torque converter clutch (TCC) solenoid has failed electrically or does not apply the clutch as commanded. The control module saw a circuit or performance fault. Meaning can vary by OEM.
Severity 3/5
Truck-relevant
Service this week
Severity
Service this week
Torque Converter Clutch Solenoid Failed
Code
P1742
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
P1742 on the Transmission system is most often faulty 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
Torque converter does not lock up, higher rpm at highway speed, poor fuel economy, higher transmission temperatures, and a check-engine light.
Common causes
- CommonFaulty TCC solenoid ($250–$700)
- CommonWiring or connector fault ($100–$400)
- OccasionalLow or dirty transmission fluid ($150–$400)
- OccasionalWorn torque converter clutch ($1500–$4000)
- RareControl module fault ($800–$2500)
How to fix
Check fluid level and condition
When to use: First step
Measure solenoid resistance and check the circuit
When to use: When fluid is good
Replace the TCC solenoid
When to use: When the solenoid is out of spec
Inspect or replace the torque converter
When to use: When the solenoid is good but lockup slips
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
Frequently Asked Questions
Can I drive with code P1742?
P1742 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 P1742 on a commercial truck?
Total repair cost ranges $100–$4000 depending on the root cause. The cheapest fix is usually the first one listed below — Faulty 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 P1742 fail a DOT inspection?
P1742 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 P1742 and related codes?
P1742 is closely related to: P1762 (Pressure Manifold Air Flow Sensor). 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 P1742 is set without the companions, the issue is more isolated.
How do I prevent P1742 from coming back after a repair?
For P1742 (Torque Converter Clutch Solenoid Failed), 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).