P0068

A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.

Safe to drive

Usually driveable, but expect hesitation. If the vehicle enters reduced power, stalls at idle, or the brake pedal becomes noticeably hard, stop driving and have it diagnosed.

Urgency

Diagnose soon

Will it pass emissions

No

If ignored

Fuel trims stay skewed, fuel economy drops and the engine hesitates or idles roughly. A large unmetered leak runs the engine lean, which raises combustion temperatures and over time stresses exhaust valves and the catalytic converter. On electronic throttle systems the condition can escalate to repeated reduced power events.

Check engine light

Solid

Clearing the light

A completed drive cycle is normally required before the monitor re-runs and the light can clear.

• Power loss, hesitation under acceleration
• Rough or unstable idle
• Increased fuel consumption
• Possible difficulty starting

Many vehicles show no symptom at all beyond the warning light. The absence of a symptom does not mean the fault is not real.

These are the causes this code can have. For the order to work through them in, see what to check first.

Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.

In order. Each of these is cheaper or faster than what follows it, and each one can make the rest unnecessary.

1. The intake ducting between the MAF sensor and the throttle body

   A split in the accordion section of the intake boot, or a loose clamp, lets in air the MAF never counted. It is one of the most common causes and is visible in under a minute, so check it first.

2. Long term fuel trim at idle and at cruise

   Trims well above +10% at idle that come back toward zero at cruise are the fingerprint of an unmetered air leak. Trims that are skewed equally everywhere point at the MAF instead.

3. The throttle plate and bore for carbon buildup

   Deposits change the actual airflow at a commanded angle without changing the reported angle, which is exactly the mismatch this code describes.

4. Every vacuum hose, the PCV system, and the brake booster hose

   These are the usual unmetered air paths. A disconnected or split brake booster hose can produce a large leak with almost no visible clue under the hood — and it also costs you vacuum brake assist, so a brake pedal that has gone hard alongside this code is a safety issue to address before driving further.

5. Whether the MAP sensor reads barometric pressure with the key on and engine off

   A clogged MAP port or a drifted sensor shows up immediately here, and it is a free check with a scan tool.

1. Read freeze frame and all stored codes together

   Tools Scan tool with freeze frame

   Note RPM, load, throttle angle and fuel trims at the moment the code set. Lean codes such as P0171 or P0174 stored alongside P0068 strongly reinforce an intake leak. Throttle position codes alongside it shift suspicion to the throttle body or its sensors.

   Expected

   A coherent picture: idle or low load with high positive fuel trims points at a leak; a wide open throttle event with low airflow points at a restriction or MAF fault

2. Check MAP against barometric pressure, key on engine off

   Tools Scan tool

   With the key on and the engine not running, the MAP reading should essentially equal the barometric pressure the PCM reports, because the manifold is open to atmosphere. A meaningful gap means the MAP sensor or its vacuum port is at fault.

   Expected

   MAP and BARO within a couple of kPa of each other; both near 101 kPa at sea level and lower at altitude

3. Compare idle airflow and manifold vacuum against expectation

   Tools Scan tool, vacuum gauge

   At warm idle in neutral, note MAF grams per second and manifold vacuum. A healthy naturally aspirated engine at idle pulls roughly 17 to 21 inches of mercury at sea level, and MAF flow at idle runs in the rough neighborhood of one gram per second per liter of displacement. These are ballpark figures, not specifications; exact values are vehicle-specific.

   Expected

   Steady vacuum in that band and airflow proportionate to engine size. Low vacuum with high airflow suggests a leak; low airflow with normal vacuum suggests MAF drift or a restriction

4. Smoke test the entire intake tract

   Tools Smoke machine, plugs and caps

   Introduce low-pressure smoke into the intake with the throttle held closed and the PCV and other openings sealed. Look for smoke at the intake boot, manifold gaskets, injector seats, throttle body gasket, brake booster hose, PCV hoses and the dipstick tube. On a turbocharged engine, test the charge piping under pressure as well.

   Expected

   No smoke escaping anywhere. Any escape point found is a confirmed unmetered air path

5. Verify throttle position and pedal position correlation live

   Tools Scan tool with graphing

   Sweep the pedal slowly and watch throttle angle track pedal angle smoothly across the full range. On drive-by-wire systems compare both accelerator pedal position signals against each other. Any dead spot, flat spot or lag identifies a sticking plate or a failing sensor.

   Expected

   Smooth, monotonic, proportional tracking from closed to wide open with no dropouts

6. Inspect the throttle bore and plate directly

   Tools Hand tools, flashlight, mirror

   Remove the intake ducting and look at the throttle plate edges and the bore behind it with the plate opened by hand. Carbon ridging around the plate is common on direct injection engines. Note whether the plate moves freely and returns cleanly.

   Expected

   A clean bore and a plate that moves without binding. Heavy deposits or a sticky plate is a finding

7. Evaluate the MAF sensor for drift

   Tools Scan tool, MAF cleaner

   With the intake proven leak-free, compare measured airflow against calculated load and RPM through a wide open throttle pull. A MAF that reads low across the range while trims sit positive is drifting. Cleaning the element with a purpose-made cleaner is the low-risk first move.

   Expected

   Airflow that scales sensibly with load and RPM, with fuel trims settling within roughly plus or minus 10%

8. Re-verify after repair with a full drive cycle

   Tools Scan tool

   Clear codes, then drive through idle, part throttle, cruise and a wide open throttle event. Confirm fuel trims settle and the correlation code does not return. If the throttle body was cleaned or replaced, check whether this vehicle requires an idle or throttle relearn procedure — many do, and the procedure varies by make.

   Expected

   No return of P0068 and fuel trims within roughly plus or minus 10% at both idle and cruise

The range is wide because the causes are wildly different in scope. A split intake boot is one of the cheapest repairs on a modern engine; an intake manifold gasket on a V-configuration engine buries several hours of labor. Diagnosis time itself is often the largest single line on the invoice, and a proper smoke test is worth paying for.

• Replacing the MAF sensor first. It is the easiest part to swap and one of the least likely causes when a leak is present, and a new MAF will read just as wrong if unmetered air is entering downstream of it.
• Skipping the smoke test because no leak is audible. Leaks past the throttle plate and small manifold gasket leaks are often silent.
• Cleaning the throttle body with a spray that attacks the coating on the bore, or with the plate forced open on a drive-by-wire unit, damaging the actuator.
• Cleaning a throttle body and not performing the relearn the vehicle requires, leaving an idle that is worse than before.
• Treating the code as an emissions annoyance on a drive-by-wire vehicle. The same plausibility logic gates reduced power mode, so it deserves prompt attention.
• Reconnecting a popped-off brake booster hose and moving on without checking why it came off, when the same failure also takes away brake assist.

• Mass Air Flow (MAF) Sensor
• Throttle Body
• Throttle Position Sensor
• Manifold Absolute Pressure Sensor
• Intake Manifold

• P0067Air Assisted Injector Control Circuit HighSeverity level 3 of 5: Diagnose soon.moderate
• P0069Manifold Absolute Pressure - Barometric Pressure CorrelationSeverity level 3 of 5: Diagnose soon.moderate

Definition

Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.

Diagnostic guidance

Written and reviewed in-house. See our editorial policy.

Review status

Reviewed

Found something wrong? Tell us — we publish corrections.