Low Fuel Shutdown (U1 Switch Open)
The DOOSAN-CODE-8 (Doosan/Ingersoll-Rand SECU portables) diesel fault code means: Low Fuel Shutdown (U1 Switch Open). This is a critical severity code.
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- Yes, but fix soon
- DIY difficulty
- moderate
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Common Symptoms
- Machine shuts down or will not crank, SECU display shows code 8
- Fuel level may genuinely be low
Probable Causes (Ranked by Likelihood)
- Fuel tank low — the U1 low-fuel switch is doing its job High
- Faulty optional U1 low-fuel sensor Moderate
- Missing T3-T4 bypass on machines WITHOUT the optional fuel sensor Moderate
Step-by-Step Diagnostic Procedure
This code set applies to SECU-display machines (7/51, 7/71, XP185, P260). Newer Tier-4-Final Doosan portables such as the P185WDOU-T4F use a DIFFERENT code set (CPR codes) — confirm which controller your machine has before acting on this page.
Check the fuel level first.
If fuel is fine: disconnect the U1 harness plug, remove U1 from the tank, and check across pins A and B with an ohmmeter while tilting the float — resistance should swing from near-infinite to near zero. That proves the shutdown switch works.
Check connectors T3 and T4, wire W013 to SECU pin 34, and W090 to splice E16.
Note: on machines without the optional fuel sensor, T3 and T4 must be connected together to bypass it — a missing bypass reads as low fuel and prevents cranking.
Frequently Asked Questions
Why will the machine not crank with code 8?
Code 8 deliberately prevents engine cranking — the SECU sees the normally closed low-fuel circuit open. If the tank has fuel, either the optional U1 float sensor failed, its wiring is broken, or on machines without the sensor the T3/T4 bypass connection is missing.
Sources
This page is built from documented references. Verify against your own service info before repair work.
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