P1704 — Turbo Charge Relief Circuit Malfunction

For Ford vehicles

transmission range circuit not indicating park/neutral during self test

powertrain (engine/transmission)

Is it safe to drive?

Drive with caution Drive gently and avoid boost. The car will likely be down on power and may be in limp mode; ignoring boost faults can overheat the engine and destroy the turbo — a far more expensive repair.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm P1704 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the turbocharger / supercharger boost control for damage, corrosion, chafing or poor contact.
Subsystem check Run the module's actuator test for the turbo charge relief if your scanner supports it — a component that does not respond to a direct command is confirmed faulty.
Subsystem check Pressure-test the intake piping for boost leaks — cracked intercooler hoses are the most common cause.
Subsystem check Command the boost control solenoid with a scanner and verify wastegate movement.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P1704 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P1704 (parts and labor, USD, independent shop rates): Repair boost leak (hoses, clamps, intercooler): $100–$400; Turbocharger replacement: $1,200–$3,500; Replace boost control solenoid or actuator: $200–$600. Overall, fixing P1704 usually costs between $100 and $3,500. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

What is the most common cause of P1704?

The most common causes are: clogged intake or exhaust (DPF/cat), faulty boost pressure sensor, vacuum or actuator line damage.

What are the symptoms of P1704?

Drivers most often notice: Check Engine Light on, black smoke under acceleration, whistling or siren noise from the engine bay, limp-home mode.

How much does it cost to fix P1704?

Repair boost leak (hoses, clamps, intercooler) — $100–$400; Turbocharger replacement — $1,200–$3,500; Replace boost control solenoid or actuator — $200–$600. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

How do I diagnose P1704 myself?

Start with a scan: confirm P1704, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the turbo charge relief, and verify the suspect component against live data before buying parts.

What does OBD2 code P1704 mean?

Turbo Charge Relief Circuit Malfunction (P1704): a powertrain (engine/transmission) fault affecting the turbocharger / supercharger boost control. Short, gentle driving to a shop is usually possible. Most often caused by clogged intake or exhaust (DPF/cat), faulty boost pressure sensor, vacuum or actuator line damage.

When your check engine light comes on and a scan tool pulls code P1704, your vehicle's engine computer has detected a problem with the turbocharger or supercharger boost system. Specifically, the module found that the turbo charge relief mechanism — the component responsible for venting excess boost pressure — is operating outside its expected parameters. This code falls under the powertrain category, meaning it relates to the engine and drivetrain rather than chassis or body electronics.

The turbo boost system works by forcing more air into the cylinders than atmospheric pressure alone would deliver. When boost pressure climbs too high, the turbo charge relief circuit (sometimes called a diverter valve or blow-off valve) vents the excess to prevent damage. The engine control unit constantly monitors this relief circuit through self-diagnostics, comparing sensor readings against factory specifications. If the system behaves erratically or fails to respond appropriately during these checks, P1704 triggers. The module also captures a freeze frame snapshot at the moment of failure, recording engine RPM, load conditions, coolant temperature, and vehicle speed — this data is crucial for pinpointing when and under what circumstances the fault occurred.

Unlike simple electrical circuit codes, P1704 indicates a broader malfunction that could originate from the component itself, its wiring, or even the control software. This means diagnosis requires a logical sequence: start with electrical integrity before considering expensive part replacements. The freeze frame data is your best starting point because it tells you exactly what the engine was doing when the fault was logged.

Common Symptoms of P1704

Illuminated check engine lamp
Noticeable black smoke from the exhaust when accelerating
Unusual whistling or siren-like noise coming from the engine bay
Vehicle enters limp-home (reduced power) mode
Higher-than-normal oil consumption

What Causes P1704?

Wiring damage or poor connector contact disrupting the boost control circuit
Internal failure of the turbo charge relief valve or blow-off valve
Faulty control module driver or outdated engine software
Boost leak somewhere in the intercooler piping or intake hoses
Restricted airflow from a clogged particulate filter or catalytic converter
Torn or disconnected vacuum lines feeding the actuator
Stuck or binding wastegate; failed boost control solenoid

How to Diagnose P1704

Connect an OBD2 scanner, confirm P1704 is stored, and record the freeze frame data — this shows engine speed, load, temperature, and speed when the fault first appeared.
Look for any other trouble codes alongside P1704. Related codes often point directly to the root cause. Also search for factory technical service bulletins specific to your make and model.
Inspect the wiring harness and connectors at the turbocharger and boost control solenoid. Look for frayed wires, corrosion, chafing from heat, or connectors that are not fully seated.
If your scan tool supports bi-directional control, run the actuator test for the turbo charge relief. A component that ignores the command is confirmed defective.
Pressurize the intake tract and listen for escaping air. Cracked intercooler hoses are the most frequently encountered source of boost loss.
Command the boost control solenoid with the scanner while observing the wastegate or diverter valve — mechanical movement should be visible and responsive.
Clear the code, then drive through conditions matching the freeze frame data. P1704 should stay cleared if the repair was successful.

Repair Options for P1704

Address the cheapest probable causes before committing to major repairs:

Fix boost leak (hoses, clamps, intercooler): $100–$400
Replace turbocharger assembly: $1,200–$3,500
Replace boost control solenoid or actuator: $200–$600

How Much Does It Cost to Fix P1704?

Total cost depends entirely on which part has failed. For P1704, typical independent shop invoices break down as follows (parts and labor, USD):

Boost leak repair: $100–$400
Turbocharger replacement: $1,200–$3,500
Boost control solenoid or actuator replacement: $200–$600

Most P1704 repairs fall somewhere in the $100 to $600 range if the issue is a simple leak or solenoid. Turbo replacement is the extreme end and should only be considered after all other possibilities are ruled out. Spending time on accurate diagnosis before purchasing parts almost always saves money.

Can You Drive with P1704?

Drive with caution and avoid hard acceleration. The vehicle may run in reduced-power mode, and prolonged operation with uncontrolled boost can lead to engine overheating or catastrophic turbocharger failure — far exceeding the cost of timely repairs.