Code
P1691
MAZDA
P — Powertrain
Turbo Pressure Control Solenoid Circuit
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring to the turbo pressure control solenoid
- Poor or corroded connector at solenoid or ECU
- Failed turbo pressure control solenoid (stuck or electrical failure)
- Faulty turbo actuator or mechanical binding
- Faulty ECU or driver circuit
- Blown fuse or poor ground
Symptoms
- MIL/Check Engine Light on
- Reduced engine power or limp mode
- Poor acceleration and slow turbo spool
- Erratic boost pressure (overboost or underboost) or boost dropouts
- Possible black smoke under load (if overfueling due to low boost)
- Stored freeze-frame data showing boost anomalies
What to check
- Read and record freeze-frame and live data (boost, commanded duty, solenoid status)
- Visual inspection of solenoid, connectors, wiring harness, and vacuum/boost hoses
- Check fuses and engine grounds related to turbo control
- Inspect for heat or chafe damage where harness passes near turbo/exhaust
- Wiggle test wiring with scan tool monitoring to reproduce intermittent faults
Signal parameters
- Expected control: ECU drives solenoid with a pulsed (PWM) ground or 12V feed; duty cycle varies 0–100%
- Typical operating voltage range at solenoid connector: 0–12 V (depending on commanded state)
- Coil resistance (approximate): commonly 10–30 ohms for many turbo solenoids — consult model-specific spec
- Command frequency: PWM commonly in the tens to a few hundred Hz (varies by design)
- Expected response: when commanded, boost/actuator position or boost sensor should change in proportion to duty cycle
Diagnostic algorithm
- Retrieve DTC and freeze-frame data; clear codes and attempt to reproduce while monitoring live boost and command signals.
- Visually inspect solenoid, electrical connector, and vacuum/boost hoses. Repair any obvious damage or loose connections.
- With ignition on (engine off), backprobe the solenoid connector: verify supply voltage (typically battery voltage or ignition-switched voltage) and that the ECU provides a switching/ground signal when commanded by a scan tool.
- Measure solenoid coil resistance with connector disconnected; compare to spec. Replace solenoid if open or out of range.
- Command the solenoid ON/OFF or vary duty via a capable scanner while observing solenoid response (audible click) and live boost/actuator movement. If no response, isolate wiring.
- Check continuity and resistance of control and ground circuits between solenoid and ECU; look for shorts to power, ground, or chassis.
- Inspect and test vacuum/boost actuator (if applicable) for free movement and leaks. Replace hoses that are cracked or leaking.
- If wiring and solenoid check good but fault persists, inspect ECU driver output for correct switching; consider ECU bench test or replacement only after other causes eliminated.
- After repairs, clear codes and perform road test under various loads to confirm fault does not return.
Likely causes
- Damaged or disconnected connector at the turbo pressure control solenoid
- Open or short in the solenoid control/ground circuit
- Failed/sticking solenoid valve
- Damaged boost/vacuum hose or external leak preventing expected response
- ECU driver circuit fault (less common)
Fault status
Status
Turbo Pressure Control Solenoid Circuit — electrical fault detected (open, short, intermittent, or unexpected response). May cause reduced boost or limp mode.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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