SANY SR220C F15 ECM Fuse and No-Start Diagnosis

A fuse that fails immediately after power-on is not merely an inconvenience. On a rotary drilling rig, it can remove the engine controller's supply, prevent starting, and encourage repeated fuse replacement without correcting the short circuit. In this field case, a SANY SR220C being prepared for export to Russia could not be started because the F15 ECM-power fuse blew whenever the electrical system was switched on.

Other machine functions remained available, so the investigation focused on the engine electrical circuit rather than a complete loss of machine power. The original report records an important diagnostic lesson: replacing the ECM did not stop the fuse from failing. The repair only succeeded after the related wiring and preheat-relay circuit were checked connection by connection.

This article is adapted from the supplied service report. It preserves the confirmed model, circuit labels, diagnostic sequence, and repair result while removing the full equipment number, personal details, and internal service information.

The Symptom Before Export

The SR220C was due to cross into Russia through Heihe. During preparation, switching on the machine immediately opened the F15 fuse that supplied the engine control module. Once the fuse failed, the engine could not start, although the report states that the machine's other available functions behaved normally.

That combination narrowed the first inspection area. A complete battery or master-power failure would normally affect more than the engine controller. Here, the repeated failure of the same protected circuit pointed toward excessive current or a short to ground downstream of F15.

Machine identified in the source: SANY SR220C with a Mitsubishi engine.
Primary symptom: F15 failed immediately when electrical power was switched on.
Operational result: the engine could not be started after the fuse opened.
Comparison evidence: other machine functions remained available.

Why the ECM Was Not the Final Answer

The initial possibilities included a failed ECM, a fault in the preheat-relay circuit, or a short in the associated wiring. The ECM was replaced during the investigation, but F15 continued to fail. That result mattered: replacing an expensive control unit did not change the symptom, so the diagnosis had to return to the power path rather than treating the new module as confirmation of the original assumption.

The technicians checked the No. 45 circuit branches below F15 and also checked the wiring associated with the K11 relay. Those checks did not reveal the fault. The remaining investigation then concentrated on K7 and its connector relationship.

List plausible causes before replacing additional components.
After any substitution, verify whether the original symptom changes.
Use the fuse designation and wire numbers to keep the inspection tied to the actual circuit.
Treat an unchanged fault after parts replacement as evidence that the assumption was incomplete.

Fuse-panel test setup used during the SR220C no-start diagnosis

The K7 Preheat-Relay Connection Revealed the Short

At K7, the report identifies the white No. 95 wire as the supply side and the red-green wire as the return connection. At the chassis connector, the No. 95 wire position was connected directly to ground. This meant the fault appeared when the cold-temperature control logic requested preheating and the ECM supplied the relay circuit.

Instead of current operating the relay as intended, the energized path was taken directly to ground. The resulting short opened F15 and removed power from the ECM circuit. The finding connected all three observations: immediate fuse failure, loss of engine starting, and normal operation in unrelated machine circuits.

The failure was associated with connector wiring, not a confirmed internal ECM defect.
Wire identification was verified at the K7 preheat relay and chassis connector.
The incorrect ground path explained why a replacement fuse failed again.
The source photographs document the fuse test setup and electrical components inspected.

SR220C engine electrical components inspected during the preheat-circuit diagnosis

Connector Correction Restored Normal Starting

The No. 95 white wire and the red-green wire were corrected at the connection described in the report. After the two positions were corrected, switching on the electrical system no longer caused F15 to fail. The key-on sequence was normal, and the engine started normally.

The decisive verification was not simply that a new fuse survived while the machine stood idle. The repair was checked through the same power-on and starting sequence that had reliably reproduced the fault before the wiring correction.

Corrective action: restore the two wires to their proper connector positions.
Power-on verification: F15 remained intact.
Starting verification: the engine started normally.
Confirmed root cause: incorrect preheat-relay circuit wiring at the connector.

What an Overseas Buyer Should Verify

For a used rotary drilling rig, a no-start condition should be documented from a cold, unassisted power-on whenever conditions allow. Ask the inspector to show battery voltage, the condition and rating of the affected fuse, whether the fuse fails at key-on or during cranking, and which other machine systems remain functional. These observations help separate a local protected-circuit fault from a broader power-supply problem.

After a wiring repair, request a continuous video of key-on, preheat indication where applicable, engine cranking, stable running, and a second restart. Photographs should show repaired connectors supported and insulated correctly rather than hidden under temporary tape. A replaced controller should also be explained: buyers need to know whether it solved the fault or was only one step in the diagnosis.

Do not accept repeated fuse replacement as a completed repair.
Confirm the fault no longer appears under the same conditions that caused it.
Record connector condition and wire identification before shipment.
Require a clear explanation whenever a high-value electronic module was replaced during diagnosis.

Diagnosis Before Replacement

This SR220C case shows why electrical diagnosis must continue when a substituted control module does not change the symptom. The fuse designation, relay path, and connector wiring ultimately provided stronger evidence than the first component assumption.

Kepler Machinery uses this evidence-led approach to evaluate and prepare used rotary drilling rigs for overseas buyers. The goal is to show not only that a machine starts, but also what failed, how the cause was isolated, and how the completed repair was verified.

Safety Note

Starting, preheat, and ECM circuits can carry high current and can be damaged by incorrect testing. Fuse substitution, continuity checks, connector repair, and engine starting must be performed by qualified technicians using the correct wiring diagram, fuse rating, insulated tools, and safe machine-isolation procedures.