SAE J1939 - Failed Engine Speed Signal
The ECM isn’t getting a valid engine speed signal from the sensor.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
The engine control module (ECM) relies on the engine speed sensor to know how fast the engine is running. If the sensor isn't working, the ECM can't control engine performance properly.
What the computer is actually seeing
The ECM expects to see a consistent voltage signal that reflects the engine speed, typically 0 to 5 volts, fluctuating based on RPM. A fault occurs when the voltage is below 0.5 volts or above 4.5 volts during normal operations.
What a healthy reading looks like
Normal engine speed signal should show a voltage varying between 0.5V (idle) to about 4.5V (maximum RPM).
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Check the engine speed sensor wiring harness for visible damage or wear. If damaged, repair or replace the harness. Decision point: If wiring is good, proceed to Step 2.
- 22. Verify the connector at the engine speed sensor for corrosion or loose connection. Clean and secure if necessary. Decision point: If connector is secure, proceed to Step 3.
- 33. Test the engine speed sensor with a multimeter. At idle, you should see a voltage close to 0.5V, increasing with RPM. If no signal or outside of 0.5V - 4.5V, replace the engine speed sensor. Decision point: If sensor is faulty, replace it; if not, proceed to Step 4.
- 44. Check the voltage and ground at the ECM connector for the engine speed signal circuit. Voltage should be present and stable. If not, investigate ECM or wiring to ECM. Decision point: Repair if faulty wiring, if good replace the ECM.
Common causes
- Faulty engine speed sensor
- Wiring issues between the sensor and ECM
- Connector problems, such as corrosion or a poor connection
- ECM malfunction or calibration issue
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with SPN 1667?
Not recommended. The engine may not run correctly, affecting drivability and safety.
Will this code come back after clearing?
Yes, if the underlying issue isn't fixed, the code will likely return.
Why does this code pair with SPN 1666?
SPN 1666 indicates data signal failure, often stemming from the same sensor issues as SPN 1667.
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