OBD-II trouble code
P0048: Turbocharger/Supercharger Boost Control Solenoid Circuit High
The module saw the boost control circuit sitting higher than it should. On this particular solenoid the cause is disproportionately oil — the connector lives where leaks land, and oil wicks along the strands inside the insulation until it reaches the terminals.
Quick facts
- System
- Powertrain
- Category
- Fuel & Air
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $40 – $900
- DIY difficulty
- Intermediate DIY
What does P0048 mean?
P0048 stores when the module tried to pull the boost control circuit down and found voltage still on it, or when the circuit read at supply level at a point in the cycle where it should have been low. In electrical terms that is either an open somewhere in the driven path, so nothing is being pulled down, or a source of voltage the module is not in control of.
Separating those two takes one test and no dismantling. With the connector unplugged and the key on, read the control wire. An open circuit and a short to power give different answers, and knowing which one you have before you start removing charge piping is worth the two minutes it costs.
Where this code differs from every other circuit-high code in the library is in what actually gets it there, and the reason is where the solenoid lives. It is mounted on or beside the engine, high in the bay, usually within a short distance of the turbocharger — which puts it directly underneath two of the most common oil leaks a turbocharged engine has: a weeping valve cover gasket and a seeping turbo oil feed or drain. Oil that lands on a connector does not simply sit on the outside. It gets past the seal, works into the crimp, and then travels: capillary action carries it between the individual strands of the conductor, inside the insulation, sometimes for a considerable distance up the loom. The result is a connector whose terminals are sitting in oil, whose seals have swollen and lost their grip, and whose contact resistance climbs until the circuit behaves as an open. It looks fine from the outside. It reads wrong every time.
The diagnostic value of knowing this is that it changes what you do when you find oil in the plug. Cleaning the terminals and pushing them back together fixes the symptom for a few weeks and no longer, because the oil already inside the wire keeps arriving and the leak that supplied it is still there. The correct repair is to cut back the affected wire to clean, dry conductor, splice in new lead, and fix the leak that caused it. Anyone who has replaced two solenoids on the same car in six months has usually met this and not recognised it.
Heat is the other contributor specific to this position. A harness that spends its life a few inches from a turbine housing sees temperatures that make insulation brittle and slowly retract crimped terminals in their housings, and both produce an intermittent open that comes and goes with engine temperature rather than with road conditions.
One planning point that materially affects the estimate. On many recent engines this solenoid is not a serviceable part on its own but forms part of an electric wastegate actuator. Establish which arrangement is fitted before quoting, because the two answers are an order of magnitude apart in price.
Common causes
- Oil contamination in the solenoid connector from a leaking valve cover gasket or turbo oil line, wicking along the conductor strands
- Swollen or displaced connector seals allowing water and oil past them
- Open circuit in the control wire from heat-embrittled insulation cracking
- Terminal retracted or spread in its housing after prolonged heat cycling near the turbine
- Short to battery voltage where the harness has chafed against a bracket or another loom
- Open winding in the solenoid coil
- Corroded crimp inside the insulation, invisible from outside
- Connector left unlatched during intercooler, charge pipe, or turbocharger work
- Failed module driver, which should be concluded only after the harness has been eliminated
Symptoms
- Check engine light with normal idle and light-throttle behaviour
- Boost that no longer follows the commanded value under load
- Reduced power or a limp mode that appears only when the engine is worked
- Fault that comes and goes with engine temperature rather than with weather or road surface
- Repeat failure a few weeks after a connector was cleaned and reassembled
- Visible oil in or around the solenoid connector
- Overboost or underboost depending on which position the actuator defaults to
- No chatter or hesitation on throttle lift, which distinguishes this from an intake-side bypass fault
Diagnostic steps
- 1.Unplug the solenoid, turn the key on, and read the control wire. Voltage present with nothing connected points to a short to power; no voltage at all points to an open in the driven path.
- 2.Pull the connector apart and look inside for oil before doing anything else. Oil in the terminals is the signature failure at this location and it changes the repair.
- 3.If oil is present, feel the wire behind the connector. Oil that has wicked into the strands leaves the insulation soft and the conductor slippery some distance back from the plug.
- 4.Do not clean and reassemble an oil-contaminated connector as the repair. Cut back to clean, dry conductor, splice in new lead, and address the leak that supplied the oil.
- 5.Identify the leak source above the connector — most often a valve cover gasket or a turbo oil feed or drain — and confirm it has been fixed, or the same fault returns.
- 6.Measure coil resistance against the manufacturer's figure with the connector off, to separate an open coil from an open harness.
- 7.Inspect the harness for heat-embrittled insulation everywhere it runs within a few inches of the turbine housing or manifold.
- 8.Check whether the terminals have retracted or spread in their housings, which produces an intermittent open that tracks engine temperature.
- 9.Note whether the fault correlates with engine temperature rather than with weather, and test in the condition where it exists rather than on a cold engine.
- 10.Confirm whether the solenoid is a separate part on this engine or integrated into an electric wastegate actuator before ordering anything.
Repair cost
$40 – $900
Repairing an oil-contaminated circuit properly — cutting back the wicked conductor, splicing in fresh lead, and renewing the connector — is $120 to $350, and the associated leak repair is a separate bill: a valve cover gasket is typically $150 to $450 and a turbo oil line $150 to $500. A standalone solenoid is $70 to $260 fitted. An integrated electric wastegate actuator assembly is $450 to $900 or more and may require calibration. The most expensive version of this code is the one paid twice, where the connector was cleaned and reconnected without dealing with the oil inside the wire or the leak above it.
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Open the Repair Cost Estimator with wiring harness / circuit repair preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.