Faulty turbocharger relief valve solenoid (boost control solenoid) or its internal coil; Damaged or disconnected electrical connector at the relief valve solenoid; Broken, corroded, or shorted wiring in the relief circuit; Vacuum or boost hose leak connected to the relief valve or actuator; Sticking or seized relief valve mechanism due to carbon buildup or wear; Failed PCM driver circuit (rare but possible after other causes are ruled out)

DTC codes / Mazda codes / P1694

P1694 · MazdaTurbo Charge Relief Circuit

Q: What does code P1694 mean?

Turbo Charge Relief Circuit. P1694 on Mazda vehicles indicates that the powertrain control module (PCM) has detected an abnormal condition in the turbocharger relief circuit, which typically controls a bypass or blow-off valve to regulate boost pressure. The PCM monitors the circuit for expected voltage or resistance and sets this code when the signal falls outside the programmed range, often due to an open, short, or faulty component.

P1694 on Mazda vehicles indicates that the powertrain control module (PCM) has detected an abnormal condition in the turbocharger relief circuit, which typically controls a bypass or blow-off valve to regulate boost pressure. The PCM monitors the circuit for expected voltage or resistance and sets this code when the signal falls outside the programmed range, often due to an open, short, or faulty component.

SystemPowertrain

Code typeMazda specific

SeverityMedium

Fix difficultyIntermediate

AreaComputer and output circuits

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Reduced engine performance or a sudden loss of boost pressure
Audible hissing or whistling from the turbocharger area during acceleration
Rough idle or stalling after heavy acceleration
Poor fuel economy or increased turbo lag

Common causes, most likely first

Faulty turbocharger relief valve solenoid (boost control solenoid) or its internal coil
Damaged or disconnected electrical connector at the relief valve solenoid
Broken, corroded, or shorted wiring in the relief circuit
Vacuum or boost hose leak connected to the relief valve or actuator
Sticking or seized relief valve mechanism due to carbon buildup or wear
Failed PCM driver circuit (rare but possible after other causes are ruled out)

How to diagnose and fix it

Inspect the relief valve solenoid and its electrical connector for looseness, corrosion, or damage
Check all vacuum and boost hoses for cracks, splits, or disconnections and repair as needed
Measure the resistance of the relief valve solenoid and compare to the manufacturer's specification
Test the wiring harness for continuity and shorts between the solenoid and the PCM
Apply vacuum or pressure to the relief valve actuator to verify smooth mechanical operation
Replace the faulty relief valve solenoid or valve assembly if electrical and mechanical tests fail
Clear the diagnostic trouble code and perform a road test to confirm the repair and ensure the code does not return

Don't overlook the relief valve solenoid

A common mistake is replacing the turbocharger itself when the actual fault is a simple vacuum leak or a failed relief valve solenoid that costs far less to fix.
The P1694 code can be set intermittently by a poor electrical connection that only acts up under vibration or temperature changes, so wiggle-testing the harness while monitoring live data is essential.
On some Mazda models, the relief valve solenoid is shared with the wastegate control circuit, and a fault in one can mimic the other, so always verify which circuit the code actually refers to using the factory service information.
Carbon buildup on the relief valve plunger can cause it to stick without setting a solenoid electrical code, so mechanical inspection is just as important as electrical testing.
After repairs, the PCM may require a relearn procedure or several drive cycles before the code will clear permanently, and simply erasing the code without fixing the root cause will lead to a quick return.

Can I keep driving with P1694?

You can usually drive the vehicle with this code, but avoid aggressive acceleration and sustained high boost until the fault is repaired, as the turbocharger may not regulate pressure correctly and could cause further damage or reduced performance.

Tools that help

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Guidance is general and written for Mazda vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.