Engine Speed Too Low
The engine is not reaching the expected RPM level.
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 computer monitors engine speed using the crankshaft position sensor. If the RPM drops below a certain threshold—usually around 500 RPM at idle—the fault code triggers, noting a low engine speed issue.
What the computer is actually seeing
The Engine Control Module (ECM) expects engine RPM to be above 500 when running. If it senses RPM dropping below that, it triggers SPN 1955.
What a healthy reading looks like
Expected RPM should be between 600-800 at idle. Under load, RPM should exceed 2000.
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.
- 1Check the engine oil level; it should be between the minimum and maximum marks on the dipstick.
- 2Inspect wiring and connectors at the crankshaft position sensor for damage, corrosion, or loose connections.
- 3Use a scan tool to monitor the engine RPM. If RPM is indeed low, proceed to the next step.
- 4Check the fuel pressure; it should be within manufacturer specifications, often around 40-60 PSI.
- 5Inspect the idle air control valve (IAC) for proper operation; a stuck IAC can prevent the engine from idling properly.
- 6If all checks are normal but the code persists, replace the crankshaft position sensor.
Common causes
- Faulty crankshaft position sensor
- Wiring issues or connector faults
- Fuel delivery problems
- Vacuum leaks
- Bad idle air control valve
- Low engine oil level
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code active?
It's not advisable to drive as engine performance could be affected, leading to stalling.
Will this code come back after I clear it?
If the underlying issue is not resolved, the code will likely return.
Why does this code appear with other codes?
Codes often indicate related issues in the same system; fix one may resolve the others.
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