What does it mean?
P1758 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: A/T Lockup Solenoid Valve 'B' Circuit Malfunction .
Symptoms
- MIL (check engine lamp) on with a transmission warning
- Torque converter lockup never applies, so engine RPM stays high while cruising
- Shudder or vibration in the lockup range under light throttle
- Engine stalls when stopping if the clutch remains applied
- Higher fuel consumption and rising transmission temperature
Likely causes
- Open or shorted lockup solenoid valve B winding
- Short to ground or short to battery on its drive circuit
- Corroded case connector or an internal harness contaminated with ATF
- Solenoid screen blocked or the plunger stuck by varnish
- Sticking lockup control valve in the valve body bore
- Degraded fluid or low line pressure preventing smooth apply and release
- Module output driver failure, considered after the circuit is proven
How to fix it
- Check fluid level, colour and smell, and correct any deficiency first
- Watch converter slip RPM on live data at a steady cruise and note whether lockup engages
- Command the lockup solenoid with a scan tool and look for the expected RPM drop
- Measure solenoid resistance at the case connector and compare with specification
- Test the drive circuit for opens, shorts to ground and shorts to battery
- Inspect the case connector, internal harness and solenoid screen for contamination
- Replace the solenoid or service the valve body, then verify smooth lockup on a road test