P016900 – Incorrect Fuel Composition: Causes, Symptoms, and Solutions

As a car service professional, one of the more confusing fault codes customers encounter—especially with flex-fuel vehicles—is P016900: Incorrect Fuel Composition. This code can trigger drivability complaints and poor fuel economy if not handled correctly. In this blog, we’ll break down what the code means, why it happens, and how your workshop can diagnose and fix it efficiently.

—

What Does Error Code P016900 Mean?

The P016900 diagnostic trouble code (DTC) indicates that the vehicle’s Engine Control Module (ECM) has detected a fuel composition reading that falls outside the expected range.

This code is most commonly found in flex-fuel vehicles (FFVs) that can run on gasoline, ethanol blends (such as E10–E85), or a mix of both. These vehicles rely on a fuel composition (ethanol content) sensor to determine how much ethanol is present in the fuel so the ECM can adjust ignition timing and fuel injection accordingly.

When the ECM receives incorrect or implausible data, it sets code P016900.

—

Common Symptoms Customers May Report When P016900 is present, drivers may experience:

🎀Check Engine Light illuminated

🎀Rough idle or engine hesitation

🎀Poor acceleration

🎀Reduced fuel economy

🎀Hard starting (especially cold starts)

🎀Engine running rich or lean

In some cases, the car may still drive normally, making this code easy to ignore—until fuel economy or performance drops significantly.

—

What Causes P016900 – Incorrect Fuel Composition?

Here are the most common causes technicians encounter:

1. Incorrect or Contaminated F HVuel

Gasoline contaminated with water

Diesel mistakenly added to a gasoline vehicle

Excessive ethanol content beyond vehicle limits

2. Faulty Fuel Composition (Ethanol) Sensor

Sensor output stuck or erratic

Internal sensor failure due to age or contamination

3. Wiring or Connector Problems

Corroded connectors

Damaged wiring harness

Poor ground or power supply to the sensor

4. Sudden Fuel Type Change

Switching from E85 to regular gasoline (or vice versa)

ECM not given enough drive time to relearn fuel composition

5. ECM Software or Calibration Issues

Outdated engine control software

ECM unable to interpret sensor data correctly

—

How to Diagnose P016900 in Your Workshop

A systematic approach saves time and avoids unnecessary parts replacement.

Step 1: Verify the Fuel

Ask the customer about recent refueling

Confirm the correct fuel type was used

Check for signs of fuel contamination

Step 2: Scan Live Data

Monitor ethanol percentage readings

Typical gasoline: ~0–10% ethanol

E85: ~70–85% ethanol

Look for values that are stuck, jumping, or unrealistic

Step 3: Inspect Wiring and Connectors

Check the fuel composition sensor harness

Look for corrosion, loose pins, or damaged insulation

Step 4: Perform a Relearn Procedure

Clear the fault code

Drive the vehicle for 10–20 minutes under normal conditions.

Welcome To Madurai Car Service🙏🏻💐