Flex fuel

GM ethanol content sensor · sensor · AFR

In-line Continental / GM ethanol sensor. One open-collector wire. Frequency is ethanol content (about 50 Hz petrol, about 150 Hz E100). Pulse width on that same wire is fuel temperature. It is not a 0–5 V sensor. Default landing is Digital 3.

Typical parts: Continental / GM 13577429, 13577379, 13577394. Same GT150 connector and the same A / B / C jobs.

Device pinout

Looking into the sensor, locking tab at the top.

• Connector: GM 3-way on the sensor body
• Layout (looking into the part): A · B · C; polarising key top

Wiring notes

• This is a 12 V Hall-style frequency sensor. Pull-up on. Do not land C on Analog Volt.
• Install in the feed line after the filter, before the rail, with flow arrows correct. Air in the body reads nonsense ethanol.
• Ground is chassis / power ground on most GM parts — not sensor ground. Confirm in the log: a floating ground looks like 0 % or 100 % stuck.
• If Digital 3 is already VSS, use Digital 4 (B3) and say so on the lid.
• Frequency is ethanol content (about 50 Hz petrol, about 150 Hz E100). Pulse width on the same wire is fuel temperature. The output is open-collector: leave the digital-input pull-up on.
• A fault frequency outside that span means air in the body or contaminated fuel, not a VE problem.

Failure modes

• Ethanol stuck at 0% or 100%: ground is open, or the signal was landed on Analog Volt.
• Ethanol jumps with injector pulse width: the ground is shared with the injector return. Move it to a clean power ground.
• Reading swings to a fault frequency (outside the 50–150 Hz petrol-to-E100 span): the sensor is full of air, or the fuel is contaminated. Flow arrows and a full body come before a trim table.

See also

• Wideband — ethanol content is not AFR. You still need a lambda sensor.