OBD-II Code P1247: Turbocharger Boost Pressure Low

What Does P1247 Mean?

P1247 indicates the Powertrain Control Module (PCM) detects the turbocharger is not producing enough pressure, a condition known as 'low boost' or 'underboost'. A turbocharger uses exhaust gases to spin a turbine that forces compressed air into the engine. The PCM sets this code when the measured intake pressure remains below the manufacturer's specified target for a set duration under load.

Technical definition: P1247 is a manufacturer-specific OBD-II code. On Ford, BMW, and Land Rover vehicles, it is defined as 'Turbocharger Boost Pressure Low'. This means the Manifold Absolute Pressure (MAP) sensor reads a boost level below the expected range for current engine speed and load. On other makes, the definition changes entirely: it indicates a fuel injector fault on older Volkswagens or an accelerator pedal issue on Acuras.

Can I Drive With P1247?

⚠️Yes, But With Caution. You can drive, but the vehicle experiences noticeably less power during acceleration and enters a 'limp mode' to protect the engine. Continuing to drive with low boost forces a rich fuel mixture that overheats and permanently damages the catalytic converter or Diesel Particulate Filter (DPF). Diagnose and repair the issue within a few days to prevent $1,000+ in secondary exhaust system damage.

Common Causes

• Boost/Intake Air Leaks (Very Common) — Cracked or disconnected hoses between the turbo and engine intake allow pressurized air to escape. Common failure points include split rubber charge air cooler (CAC) boots, loose T-bolt clamps, or cracked plastic intake manifolds (notably on Land Rover TDV6 engines).
• Exhaust Leaks Before the Turbo (Very Common) — Leaks in the exhaust manifold or up-pipes bleed off the exhaust gas energy required to spin the turbo turbine. This is the primary failure point on Ford 7.3L Power Stroke engines at the up-pipe collector connection.
• Faulty Exhaust Back Pressure (EBP) Sensor or Tube (Very Common) — On diesel engines like the Ford 7.3L, the EBP sensor dictates wastegate control. A clogged soot tube or failed sensor sends falsely high pressure readings to the PCM, which responds by opening the wastegate and dumping boost pressure.
• Faulty Manifold Absolute Pressure (MAP) Sensor (Common) — The MAP sensor measures actual boost pressure. A soot-clogged sensor or a leaking reference hose sends artificially low readings to the PCM, triggering the code even when the turbocharger operates perfectly.
• Sticking or Malfunctioning Wastegate (Common) — The wastegate diverts exhaust gas away from the turbine to limit boost. A wastegate stuck open by mechanical binding or a failed actuator allows exhaust to bypass the turbine entirely, preventing pressure buildup.
• Faulty Wastegate Control Solenoid/Vacuum Lines (Common) — This solenoid (pressure converter) directs vacuum to the wastegate actuator. Failed solenoids or cracked, brittle vacuum lines (highly common on BMW diesels) prevent the wastegate from closing, resulting in low boost.
• Failing Turbocharger Internals (Less Common) — Worn journal bearings, damaged turbine blades, or blown oil seals prevent the turbo from spinning efficiently. This is diagnosed only after ruling out all intake and exhaust leaks.
• Restricted Air Intake or Exhaust (Less Common) — A severely packed engine air filter starves the turbo compressor. Conversely, a clogged DPF creates excessive exhaust backpressure that chokes the turbine's ability to spin.

Symptoms

• Check Engine Light On — The PCM illuminates the Check Engine Light immediately upon logging the P1247 code.
• Severe Power Loss (Limp Mode) — The vehicle accelerates sluggishly and struggles to maintain speed on inclines or while towing.
• Audible Hissing or Whistling — A pressurized intake leak creates a loud hissing sound from the engine bay that increases in volume as engine RPM and load increase.
• Black or Grey Exhaust Smoke — Low boost creates a rich air-fuel ratio (excess fuel, insufficient air), resulting in thick black or grey smoke from the tailpipe during acceleration.
• Decreased Fuel Economy — The engine burns excess fuel to compensate for the lack of compressed air, dropping fuel efficiency by 10-25%.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this code.

Common Fixes & Costs

• Repairing Intake/Boost Leaks — Parts: $20-$600, Labor: $100-$2,000, ~1.5 hr book time (DIY)
  Ford F-250/F-350 7.3L (1999-2003): OEM YC3Z-6K786-DA (Alt: Mishimoto MMHOSE-F73-99BK)
  Land Rover Discovery 4 / RRS 3.0L TDV6: OEM LR179200 (Alt: Britpart DA7014)
• Replacing EBP Sensor and Tube — Parts: $40-$150, Labor: $100-$250, ~1.2 hr book time (DIY)
  Ford F-250/F-350 7.3L (1997-2003): OEM 4C3Z9J460B (Alt: Alliant Power AP63403)
  Ford F-250/F-350 7.3L (1999-2003): OEM 1C3Z9D477AA (Alt: Dorman 904-220)
• Replacing MAP Sensor — Parts: $50-$200, Labor: $50-$150, ~0.5 hr book time (DIY)
  Ford F-250/F-350 7.3L (1999-2003): OEM F81Z-9F479-BA (Alt: Bosch 0261230044)
• Replacing Wastegate Actuator or Solenoid — Parts: $75-$400, Labor: $150-$500, ~2.5 hr book time (Intermediate)
  BMW 335d / X5 xDrive35d (M57 Engine): OEM 11658509323 (Alt: Pierburg 7.02213.04.0)
• Replacing Turbocharger — Parts: $900-$2,800, Labor: $600-$1,200, ~8 hr book time (Professional)

DIY vs Professional

• Repairing Intake/Boost Leaks (CAC Hoses) — Beginner:
• Replacing EBP Sensor and Tube — Beginner:
• Replacing MAP Sensor — Beginner:
• Replacing Wastegate Solenoid/Vacuum Lines — Beginner:
• Repairing Land Rover TDV6 Intake Manifold — Beginner:
• Replacing Turbocharger — Beginner:

Used vs. New Parts: Buying Guide

When a used part is worth it: Purchase used OEM parts for high-cost assemblies like turbochargers or Land Rover intake manifolds when repairing older vehicles where new part costs exceed the vehicle's value.

Donor-vehicle mileage cap: roughly under 90000 miles for the part to have meaningful remaining life.

Donor quality checklist:

• Verify the donor vehicle was salvaged for collision damage, not engine failure.
• Inspect used turbos for axial shaft play, chipped turbine fins, and oil coking.
• Ensure exact part number matches, as superseded numbers alter fitment.

Decision logic:

• If The part is a sensor, vacuum line, or rubber CAC hose. → Buy new. Used rubber and electronics offer zero reliability savings.
• If The part is a turbocharger and the vehicle has 150,000+ miles. → A remanufactured turbocharger offers new bearings and a warranty for half the price of a new OEM unit.

Warranty tradeoff: Used parts carry 30-90 day part-only warranties. If a used turbo fails, you pay the 8-hour labor bill twice.

Worst-case if a used part fails: 1200

What Happens If You Wait — Timeline

1. 0-1 month: Code sets. Performance loss is noticeable on hills. A minor boost or exhaust leak begins. (MPG impact: 5%% · Added cost: $50 in wasted fuel.)
2. 1-4 months: Engine runs rich, emitting black smoke. High exhaust gas temperatures (EGTs) stress exhaust components and coat sensors in soot. (MPG impact: 15%% · Added cost: $200 in wasted fuel and fouled sensors.)
3. 4-9 months: Sustained high EGTs melt the catalytic converter substrate or clog the DPF, forcing constant regeneration cycles. (MPG impact: 25%% · Added cost: $2,000 for DPF or catalyst replacement.)
4. 9+ months: Extreme exhaust backpressure blows turbocharger oil seals or causes catastrophic internal engine damage. (MPG impact: 50%% · Added cost: $5,000+ for a new turbocharger and exhaust system.)

Cost of Not Fixing It

• Short-Term (0-3 months): Fuel economy drops by 10-15%. The engine runs rich, coating exhaust sensors and the EGR valve with heavy soot. (Added cost: 50-150)
• Medium-Term (3-9 months): Sustained high exhaust gas temperatures (EGTs) overheat the catalytic converter and clog the Diesel Particulate Filter (DPF), forcing constant regeneration cycles. (Added cost: 1000-3500)
• Long-Term (9+ months): A completely clogged DPF creates extreme exhaust backpressure, blowing turbocharger oil seals or causing catastrophic internal engine damage. (Added cost: 2500-10000)

Diagnosis Steps

1. Check for Accompanying Codes
   Scan for related codes. MAP sensor faults (P0236), EBP sensor faults (P0470-P0478), MAF correlation errors (P006A), or generic underboost (P0299) pinpoint the failing subsystem immediately.
   Tools: OBD-II Scanner (Beginner)
2. Visual Inspection of Air and Exhaust Paths
   Inspect all intake hoses, intercooler pipes, and clamps for cracks or oil residue indicating a leak. Check exhaust manifolds and up-pipes for black soot trails, which confirm pre-turbo exhaust leaks.
   Tools: Flashlight, Mirror (Beginner)
3. Live Data Analysis Under Load
   Monitor Desired Boost, Actual Boost (MAP), Wastegate Duty Cycle, and Exhaust Back Pressure (EBP) during a test drive. If Desired Boost is high but Actual Boost is low while Wastegate Duty Cycle is maxed (>80%), the PCM is demanding boost but a mechanical leak or turbo failure prevents it.
   Tools: Advanced Scan Tool with Live Data Graphing (Advanced)
4. Perform a Pressurized Smoke Test
   Inject high-pressure smoke into the intake system (15-20 PSI) with the engine off. This definitively exposes microscopic cracks in rubber boots or plastic manifolds that visual inspections miss.
   Tools: Boost Leak Tester or Smoke Machine (Intermediate)
5. Inspect and Test EBP Sensor and Tube (Ford Specific)
   Remove the EBP sensor and its exhaust manifold tube. Clean the tube with a wire brush or replace it if rusted. Verify the KOEO (Key On, Engine Off) scan tool reading for EBP matches MAP and BARO (approx. 14.7 PSI at sea level).
   Tools: Scan Tool with Live Data, Basic Hand Tools (Intermediate)
6. Test MAP Sensor Voltage
   Back-probe the MAP sensor. Verify a 5V reference and <0.1V ground. The signal wire must read atmospheric pressure at KOEO (1.5-1.7V at sea level) and increase smoothly as throttle is applied. A static voltage indicates a dead sensor.
   Tools: Multimeter, Scan Tool with Live Data, Back-probe Kit (Advanced)
7. Test Wastegate Control Solenoid and Vacuum Lines
   On vacuum-actuated systems (BMW), apply 7 inHg of vacuum to the wastegate actuator to ensure it moves and holds pressure. Test the control solenoid's resistance (typically 10-30 ohms) and use a bidirectional scanner to command it on/off, listening for a click.
   Tools: Multimeter, Bidirectional Scan Tool, Hand Vacuum Pump (Advanced)
8. Inspect Turbocharger Internals
   Remove the intake tube. Check the turbine shaft for axial (in-and-out) play, which must be near zero (<0.004 inches). Spin the compressor wheel by hand; any housing contact or grinding confirms a destroyed turbocharger.
   Tools: Basic Hand Tools, Feeler Gauges (Advanced)

When This Code Triggers (Freeze-Frame Conditions)

• Engine Coolant Temp: 180-210°F (82-99°C) (The engine must reach full operating temperature for the PCM to run the boost diagnostic monitor.)
• Engine RPM: 1800-2800 RPM (The code sets during steady-state cruising or moderate acceleration, rarely at idle.)
• Engine Load: 40-70% (Triggered when the PCM commands boost under moderate load but fails to see the expected pressure response.)
• Boost Pressure Difference: >4 psi below desired (On Ford vehicles, the code sets when actual boost remains 4 PSI below desired boost for 5 continuous seconds.)

Related Codes

• P0299 — The generic SAE code for 'Turbocharger Underboost'. P1247 is the manufacturer-specific equivalent. The diagnostic approach is identical.
• P006A — 'MAP - Mass or Volume Air Flow Correlation'. Frequently pairs with P1247 on Land Rovers, indicating a massive boost leak where measured intake air escapes before reaching the manifold.
• P1248 — 'Turbocharger Boost Pressure Not Detected'. Indicates a complete lack of boost signal, pointing to a blown-off charge pipe or a dead MAP sensor rather than a minor leak.
• P0236 — 'Turbocharger Boost Sensor A Circuit Performance'. Points directly to an electrical fault in the MAP sensor circuit, which causes the PCM to falsely trigger P1247.

Climate & Environmental Factors

• High Altitude: Lower atmospheric pressure forces the turbocharger to spin faster to achieve target boost levels. This added stress exposes weak CAC boots and minor leaks that remain hidden at sea level. Ensure MAP, EBP, and BARO sensors read identically at KOEO (approx. 12.2 PSI at 5,000 ft).
• Extreme Cold and Snow: Heavy, wet snow packs into the air intake on 2011-2016 Ford 6.7L engines, starving the turbo and triggering P1247 (addressed in TSB 11-9-16). Sub-zero temperatures also turn rubber CAC boots and vacuum lines brittle, causing sudden cracks.

How to Talk to a Mechanic About This Code

Say this: "I have a P1247 low boost code. I want to authorize one hour of diagnostic time to perform a pressurized smoke test on the intake system to find leaks before we discuss replacing any parts."

Directs the mechanic to the most common failure point (leaks) and prevents them from immediately quoting a $2,500 turbocharger replacement based solely on the code.

Avoid saying:

• 'My truck is slow, I think the turbo is bad.'
• 'Just fix the check engine light.'
• 'Do whatever you think is necessary.'

Questions to ask before authorizing the repair:

• Did the smoke test reveal a leak? Can you show me exactly where it is?
• What were the live data readings for MAP and EBP during your test drive?
• Before replacing the turbo, did you confirm excessive shaft play or visible damage to the turbine wheels?

Where to Take It: Dealer vs Independent vs Chain

• Dealer: Use only for in-warranty vehicles or highly complex European models. Too expensive for common truck repairs.
  Best for: Vehicles under powertrain warranty., Complex European models (Land Rover, BMW) requiring proprietary software updates or TSB access.
  Downsides: Labor rates are 50-100% higher than independent shops., Tendency to replace entire expensive assemblies rather than individual failing components. (Typical cost: +50% vs. baseline)
• Independent Shop: The best option. A reputable diesel or European specialist diagnoses P1247 accurately for half the dealer cost.
  Best for: Out-of-warranty vehicles, especially Ford Power Strokes., Diesel specialty shops familiar with specific engine failure patterns.
  Downsides: Diagnostic capability varies; ensure they own a high-pressure smoke machine. (Typical cost: +0% vs. baseline)
• Chain Shop: Avoid entirely for diagnostics. They lack the specialized tools and experience required for turbo systems.
  Best for: Replacing a specific, easily accessible sensor if the diagnosis is already 100% confirmed.
  Downsides: Technicians lack experience with complex turbocharger diagnostics., High risk of misdiagnosing a $50 leak as a $3,000 turbo failure. (Typical cost: -10% vs. baseline)

When to Walk Away From the Repair

Sell or trade the vehicle if the repair estimate exceeds 50% of its private-party value.

• Car worth $6000, fix is $3200: Walk away. The repair exceeds half the vehicle's value.
• Car worth $15000, fix is $2500: Fix it. The repair restores significant value and performance.

What Scan Tool You Need for This Code

Minimum: A scanner capable of reading manufacturer-specific codes and displaying live data PIDs for MAP, EBP, and Desired Boost.

A $20 code reader only displays 'P1247'. It cannot show the live sensor data required to differentiate between a mechanical leak, a dead sensor, or a failed turbocharger.

Budget: FORScan Lite with OBDLink MX+ (~$85) — The absolute best choice for Ford vehicles. Monitors all proprietary Ford PIDs (MGP, EBP) and runs critical diagnostic tests like injector buzz tests.

Mid-range: BlueDriver Pro or Innova 5610 (~$120-350) — Provides comprehensive live data graphing. The Innova adds bidirectional control to actively test electronic wastegate actuators without disassembly.

Professional: Autel MaxiCOM MK808 (~$450-700) — Offers OEM-level bidirectional control to command wastegate solenoids and view detailed data streams essential for complex European diagnostics.

Rent vs buy: Buy. Auto parts stores read codes for free but do not provide live data. A capable scanner pays for itself by preventing a single misdiagnosed turbo replacement.

How to Clear the Code After You Fix It

1. Clear the DTCs using an OBD-II scan tool.
2. Perform a complete drive cycle to run the vehicle's readiness monitors and confirm the repair.

Drive cycle (~30 minutes): Start the engine cold. Idle for 3 minutes. Drive in stop-and-go traffic for 10 minutes. Accelerate smoothly to 55-60 mph and maintain steady highway speed for 10 minutes.

Readiness monitors affected: Catalyst Monitor, Evaporative System (EVAP) Monitor, Oxygen (O2) Sensor Monitor, EGR System Monitor

Before emissions retest: drive at least 50 miles to fully set monitors.

Watch out for:

• Clearing the code without fixing the leak guarantees the Check Engine Light returns under the next heavy acceleration.
• Disconnecting the battery erases all readiness monitors, causing an automatic emissions test failure until a full drive cycle completes.

Will This Fail Emissions / State Inspection?

Yes — this code typically fails an OBD-II emissions inspection.

• California: An active P1247 triggers an automatic failure. All readiness monitors must read 'Ready' post-repair before re-testing.
• New York: Causes automatic OBD-II failure. Vehicles 2001 and newer may pass with exactly one 'Not Ready' monitor after clearing codes.
• Texas: Fails inspection in the 17 emissions-testing counties. A full drive cycle is required after clearing the code.

Most Commonly Affected Vehicles

• Ford F-250/F-350 Super Duty (1999-2003) — Extremely common on the 7.3L Power Stroke. Causes are almost exclusively aging CAC boots, exhaust up-pipe leaks, or a clogged EBP sensor tube.
• Land Rover LR4 / Discovery 4, Range Rover Sport (2010-2016) — On 3.0L TDV6/SDV6 models, P1247 is frequently caused by a cracked plastic intake manifold throttle body Y-piece.
• BMW 335d, X5 xDrive35d (2009-2013) — Primary causes are degraded rubber vacuum lines controlling the wastegate or a failed pressure converter solenoid.
• Ford F-Super Duty (6.7L) (2011-2016) — Low boost is often a symptom of the PCM derating the engine due to unrelated emissions faults. TSB 11-9-16 notes snow packing the air filter causes this code.
• Volkswagen Jetta, Golf, Passat (TDI) (1998-2006) — On older TDI models, P1247 means 'Needle Lift Sensor (G80): Open or Short to Plus'. This is a #3 fuel injector fault, completely unrelated to boost.
• Acura TL, TSX (2004-2008) — P1247 indicates an 'Accelerator Position Sensor 2 Circuit Malfunction', requiring gas pedal sensor replacement. Unrelated to turbochargers.

Manufacturer-Specific Notes

• Ford: On 7.3L Power Strokes, inspect CAC boots, exhaust up-pipes, and the EBP sensor tube before testing the turbocharger. These three items account for 90% of P1247 faults.
• Land Rover: A P1247 code accompanied by a hissing noise under load on a 3.0L TDV6 guarantees a cracked plastic intake manifold. Refer to TSB LTB00445V3.
• BMW: Vacuum lines controlling the turbo wastegate crack invisibly under the cloth braiding. Replacing all vacuum lines is mandatory preventative maintenance when diagnosing low boost.
• Volkswagen/Audi: P1247 means 'Needle Lift Sensor Circuit Open/Short To Positive'. This is a fuel injector sensor issue and has nothing to do with the turbo system.

Real Owner Stories

2013 Land Rover Discovery 4 with ~150K miles

Vehicle entered 'Restricted Performance' mode on hills. Codes P1247 and P006A present.

Outcome: A high-pressure smoke test revealed a split in the plastic intake manifold. Replacing the manifold resolved both codes.

Lesson: On Land Rover 3.0L diesels, P1247 combined with P006A guarantees a cracked intake manifold. Never replace sensors before performing a smoke test.

2001 Ford F-250 7.3L Power Stroke with 135K miles

Truck lacked power, generating only 10 PSI of boost. Check Engine Light was intermittent.

Outcome: Replacing the oil-fouled ICP sensor restored power and eliminated the low boost condition.

Lesson: A failing ICP sensor on a 7.3L mimics turbo failure. Always check the ICP connector for oil intrusion when diagnosing performance issues.

2008 BMW 335d with 120K miles

Severe turbo lag and sluggish acceleration. P1247 was intermittent.

Outcome: One pressure converter failed to hold vacuum when energized. Replacing the Pierburg solenoid and all vacuum lines restored full boost.

Lesson: BMW diesel vacuum lines degrade invisibly. Testing the pressure converters and replacing all lines is the definitive fix for elusive low boost.

How to Prevent This Code From Triggering

• Idle the engine for 60 seconds before shutdown (Every drive) — Immediate shutdowns coke the oil inside the turbo's bearing housing. Idling allows the turbo to cool and oil to circulate, preventing bearing failure.
• Clean or replace the EBP sensor tube (Ford 7.3L) (Every 100,000 miles) — The metal tube clogs with hard carbon, sending false readings to the PCM that force the wastegate open.
• Replace all turbo vacuum lines (BMW Diesels) (Every 80,000 miles) — Rubber hoses become brittle from heat cycles, causing invisible vacuum leaks that disable wastegate control.
• Inspect and tighten CAC boots and T-bolt clamps (Every oil change) — Oil vapors soften rubber boots over time. Tightening clamps prevents hoses from blowing off under peak boost.

Frequently Asked Questions

What is the most common misdiagnosis for P1247?

Replacing the turbocharger without performing a pressurized smoke test is the most expensive mistake. Mechanics often blame the turbo when the actual culprit is a $50 leaking hose or a cracked plastic manifold. Always prove the intake tract is sealed before condemning the turbocharger.

I hear the turbo whistle, so how can the boost be low?

The turbo spinning and whistling confirms it is moving air, but a leak between the compressor and the engine allows that pressurized air to escape. You hear the turbo working harder to compensate, but the engine never receives the boost.

What is a boost leak test?

A diagnostic test where the intake system is sealed and pressurized with 15-20 PSI of compressed air or smoke. This forces air out of microscopic cracks or loose clamps, making leaks visible or audible.

My truck has a P1247 but feels like it has full power. What is wrong?

The fault is intermittent, meaning the PCM detected low pressure for only a brief moment. This points to a failing sensor (like the MAP or EBP) sending a momentary bad reading, rather than a permanent mechanical leak.

Can a clogged air filter cause P1247?

Yes. A severely restricted air filter starves the turbocharger compressor, preventing it from building adequate manifold pressure.

Is fixing a P1247 code expensive?

Costs range from $50 for a loose clamp to $3,000 for a failed turbocharger or Land Rover intake manifold. Accurate diagnosis dictates the final price.

Will an aftermarket tuner cause a P1247 code?

Tuners demand higher boost pressures, which easily blow off weakened hoses or expose pre-existing microscopic leaks that remained hidden under stock pressure levels.

What is the difference between P1247 and P0299?

P0299 is the generic SAE code for 'Turbocharger Underboost', while P1247 is a manufacturer-specific code. On Ford and BMW, P1247 shares the same low-boost definition but uses stricter trigger criteria. Always look up the exact definition for your specific make and model to avoid misdiagnosis.

Key Takeaways

• P1247 indicates the turbocharger is underperforming, caused by an intake boost leak or an exhaust leak in 80% of cases.
• Expect a severe drop in engine power, an illuminated Check Engine Light, and audible hissing from the engine bay under heavy acceleration.
• Perform a pressurized smoke test on the intake system first; visual inspections miss microscopic cracks in charge air cooler (CAC) boots.
• Verify your manufacturer's specific definition for P1247, as it means 'Low Boost' on Ford and BMW, but indicates a faulty fuel injector sensor on older Volkswagens.
• Driving with an active P1247 code forces a rich fuel mixture that will permanently damage a $2,000 Diesel Particulate Filter (DPF) within a few months.