Code Definition

P1121 — Ignition Control Module 4X Circuit, or TPS Out of Range

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

About P1121

P1121 is a manufacturer-specific powertrain diagnostic trouble code recorded for GM vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P1121 is stored, the module has detected a plausibility fault — the measured value is in the electrical range but is not consistent with expected operating behaviour.

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.

P1121 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 General Motors specific code covers two related fault areas, the Ignition Control Module (ICM) 4X reference circuit and the Throttle Position Sensor (TPS) signal. The 4X reference is a crankshaft based signal of four pulses per revolution that the ignition module passes to the Powertrain Control Module (PCM) for ignition timing, while the TPS reports throttle plate angle as a variable voltage. P1121 sets when the PCM sees the TPS signal voltage outside its valid operating range, usually an intermittent high reading, or detects a problem in the 4X reference circuit. Because the TPS feeds f...

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