DTC P008B00 – Low Fuel Pressure (Low Pressure Circuit Too High / Low Pressure Fuel System Pressure Too High).

🔧 DTC P008B00 – Low Pressure Fuel System Pressure Too High

🔍 What the Code Means

The ECM detects that the low-pressure fuel supply (from tank to high-pressure pump) is higher than the calibrated limit.
This usually indicates a restriction, stuck pressure regulator, sensor fault, or wiring issue.

📌 Common Symptoms

Hard starting

Rough idle

Fuel smell near engine or tank

Poor acceleration

High-pressure fuel pump (HPFP) noise

Reduced power mode (in some cars)

🛠️ Possible Causes

1. Low-pressure fuel pump issues

Pump delivering too much fuel pressure

Incorrect pump type fitted

Faulty internal regulator

2. Fuel pressure regulator fault

Regulator stuck closed → pressure rises

Regulator filter clogged

3. Fuel pressure sensor failure

Sensor giving incorrect high readings

Sensor wiring/connector damaged

4. Fuel return line blockage

Kinked, pinched, or clogged return line

Blocked fuel filter (return-style systems)

5. Fuel contamination

Diesel contamination in petrol engines or vice versa

Excess debris blocking return flow

6. ECU reading error (rare)

🔧 Step-by-Step Diagnostic Procedure (Workshop Guide)

1. Scan Tool Live Data

Check:

Low-pressure fuel pump (LPFP) actual pressure

LPFP desired pressure

High-pressure fuel pump inlet pressure.
👉 If actual pressure > desired pressure, continue diagnosis.

2. Check Low-Pressure Fuel Pump Operation

Measure pressure at the low-pressure fuel line (before HPFP)

Most petrol: 3–6 bar

Most diesel: 4–8 bar

If pressure is too high, the LPFP or regulator is faulty.

3. Inspect the Fuel Pressure Regulator

Located on pump module or fuel rail Check for:

Stuck regulator valve

Electrical control issues (for electronic regulators)

If stuck closed, pressure will rise → Replace regulator.

4. Check Fuel Pressure Sensor (Low Pressure)

Inspect:

Connector pins for corrosion

Wiring for short to power/ground

Compare sensor reading with mechanical gauge

If mechanical pressure is OK but scanner shows high → sensor faulty.

5. Inspect Fuel Return Line

Look for:

Blockage

Kinked line under vehicle

Debris in fuel tank return valve

A blocked return will cause high pressure.

6. Check Fuel Filter

If filter is clogged, pump overworks and pressure rises → Replace filter.

7. Check for Fuel Contamination

Drain a sample:

Look for metal particles (damaged pump)

Water/diesel/petrol mix

🔧 Most Common Fixes

✅ Replace faulty low-pressure fuel regulator
✅ Replace low-pressure fuel pump
✅ Replace or clean clogged fuel filter
✅ Repair wiring to fuel pressure sensor
✅ Replace faulty low-pressure fuel pressure sensor
✅ Clear kink/blockage in return line
✅ Clean tank and flush contaminated fuel.

Welcome To Madurai Car Service 💐🙏.