🧊 Holden Barina Cooling Fan Fault – ECU Failure Diagnosed

A 2005 Holden Barina recently came into the workshop with a fault where the engine cooling fan wasn’t operating correctly. The spanner warning light was illuminated on the dash, and the engine felt hotter than usual during normal driving.

🔎 Diagnostic Process

We began by scanning the vehicle using factory-level diagnostics. The ECU had stored the following fault codes:

• P1481 – Fan Relay 1 Signal Low / Open Circuit

• P1482 – Fan Relay 2 Signal Low / Open Circuit

• P1483 – Fan Relay 3 Signal Low / Open Circuit

We then tested the fan circuits manually. Each fan relay was removed and individually grounded — confirming the fans operated correctly. Power supply and continuity across all relevant wiring was also confirmed to be intact.

To further test the system, we unplugged the engine coolant temperature sensor, which triggered the ECU’s failsafe mode — and the fans came on immediately. This confirmed the ECU was still capable of running the fans, but only under emergency conditions.

🧠 Root Cause Identified

Using the wiring diagram, we traced the ECU outputs responsible for controlling the fan relays. These pins are designed to ground the relay coils to switch the fans on during normal operation. Back-probing those ECU terminals revealed no ground signal was being sent, even when conditions called for fan activation.

This confirms an internal fault within the ECU — specifically, the transistor circuitry responsible for grounding the fan relay control circuits.

An interesting note, the ECU multiplug had dielectric grease in it, indicating that someone likely has been chasing this issue prior. Using dielectric grease on module plugs is a no go, they don't need it, on these connectors it can cause more harm than good.

🛠️ Outcome

The vehicle requires an ECU repair or replacement to restore normal cooling fan function. All other components — fans, relays, wiring, and power feeds — are confirmed to be operating correctly.