Diesel Heater E08 Fault Code: Fuel Pump Short Circuit — Diagnosis and Fix
Short answer: E08 on an HLN diesel heater means the ECU has detected a short circuit on the fuel metering pump (FMP) circuit. On 8kW rotary-switch models without a screen, the same fault is flashed as blink code 01000. The diagnosis below is from HLN's factory service documentation and takes about ten minutes with no special tools.
What E08 means
The ECU monitors the current through the fuel-pump circuit. When the current indicates a short — in the pump coil itself or in the wiring harness — the heater raises E08 and stops fuel delivery for safety. The fault is in one of three places: the pump, the harness, or (rarely) the ECU. The test below separates them.
Factory diagnosis: three steps in order
- Disconnect the fuel pump connector and restart the heater. If E08 is no longer displayed, the pump itself is defective — replace the fuel metering pump.
- If E08 is still displayed with the pump disconnected, the short is not in the pump. Disconnect the main harness from the heater and inspect the harness for a short circuit (chafed insulation, pinched wires, moisture in connectors).
- If no short is found in the harness, test the ECU and replace it if necessary.
The logic matters: if the code clears when the pump is unplugged, the pump is the problem. If the code stays, the problem is upstream — do not replace the pump.
Quick coil check with a multimeter
You can confirm a pump-coil short with a resistance measurement at the pump connector (20 °C):
- Air heater pump, 12 V: 8.9 ± 0.6 Ω
- Coolant heater pump, 12 V: 5.5 Ω; 24 V: 22 Ω
A reading near zero confirms a shorted coil.
FAQ
Does E08 mean my heater is out of fuel?
No — running out of fuel typically raises E13 (no flame). E08 is electrical: a short circuit on the pump circuit.
Can I keep running the heater with E08?
The heater will not run: fuel delivery is stopped for safety until the fault is cleared.
My 8kW heater has no screen — how do I see this code?
Count the status-light flashes: E08 is 01000 — one short flash, one long, then three short (long = 1, short = 0).
All HLN fault codes in one place: HLN Diesel Heater Error Codes Explained (E01–E32). Source: HLN factory service manual and controller manual (2026 revised editions).