P00C6-00 – Fuel Rail Pressure Too Low During Engine Cranking

Meaning:

The ECM detects that during engine cranking, the actual fuel rail pressure is much lower than the commanded value.
This indicates a fuel supply issue, high-pressure pump problem, or starting system issues.

✅ Common Causes

Low-side supply (most common)

Empty or low fuel

Weak in-tank fuel pump

Blocked fuel filter / strainer

Fuel pump control module fault

Voltage drop to fuel pump (corroded connectors, weak battery)

High-pressure side

HP pump worn or failing

HP pump control valve stuck open

Pressure regulator stuck open

Leaking injector(s)

Sensor / electrical

Faulty fuel rail pressure (FRP) sensor

Wiring issues to FRP sensor

ECM fault (rare)

🔧 Step-By-Step Diagnosis (Professional Workflow)

1. Check Battery & Cranking Speed

⚠ Low cranking RPM causes low fuel pressure.

Minimum cranking voltage: >9.6V

Cranking speed: >180–220 rpm

If low → charge/replace battery, check starter.

2. Scan Live Data During Cranking

Check the following:

Parameter Normal Range If abnormal

Commanded rail pressure 25–35 MPa (250–350 bar) —
Actual rail pressure Should reach >20 MPa within 2–3 seconds If below → continue diagnosis
Low-side pressure 4–6 bar (gasoline), 5–7 bar (diesel) Low → problem with lift pump or filter

If actual rail pressure never rises → suspect fuel supply or HP pump.

3. Check the Low-Pressure Fuel System

A. Fuel pump prime test

Turn ignition ON → observe fuel pressure rise.

If no pressure:

Check fuel pump relay

Check fuel pump fuse

Check wiring voltage (should be battery voltage)

B. Fuel filter restriction

Clogged fuel filter is one of the top causes for P00C6.

Replace filter if >15,000 km old

Check water contamination in diesel

4. High-Pressure Pump Tests

Symptoms of HP pump failure:

Rail pressure rises slowly

Pressure drops immediately after start

Metal debris in fuel

Checks:

Measure HP pump inlet pressure

Command pump control valve (if scan tool allows)

Check pump cam lobe for mechanical wear (diesel engines)

5. Check for Injector Leakage

Leaking injector = rail pressure cannot build during cranking.

Test:

Perform a return flow test (diesel)

Disable injectors and observe pressure rise

Look for fuel dripping in cylinders (gasoline DI)

If excessive return → replace faulty injector.

6. Fuel Rail Pressure Sensor Check

Compare sensor reading with mechanical gauge if possible

Inspect connector for corrosion

Check 5V reference, signal, and ground

Incorrect readings may trigger P00C6.

7. Electrical & Ground Checks

Check fuel pump module ground points

Confirm continuity for FRP sensor wiring

Check HP pump valve control wiring

Electrical issues often cause intermittent low pressure.

🛠 Top 5 Most Common Fixes

1. Replace clogged fuel filter

2. Replace failing in-tank low-pressure pump

3. Repair wiring/ground to pump module

4. Replace faulty high-pressure pump

5. Replace leaking fuel injectors (high return flow)

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