Code Definition

P166F — Glow Plug Control Module Circuit Short

System: Powertrain  |  Type: Manufacturer-Specific  |  Make: Toyota

About P166F

P166F is a manufacturer-specific powertrain diagnostic trouble code recorded for Toyota vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P166F is stored, the module has detected a short-circuit (voltage pulled to ground or to supply) in the monitored circuit; and a signal or supply voltage lower than the expected operating range.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

P166F is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

This code is set when the engine control module (ECM) or the glow plug control module detects a short circuit in the glow plug control module circuit. On a diesel engine the glow plug control module regulates current to the glow plugs during cold starts and preheating. A short, either to ground or to voltage, disrupts normal operation and can cause insufficient preheating, harder or slower cold starting, rough running just after a cold start, a glow plug warning lamp, and an illuminated malfunction indicator lamp. The fault usually lies in the module wiring, a shorted glow plug, or the module ...

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