Engine Retarder Control Valve Position
The Engine Retarder Control Valve position sensor is out of range or malfunctioning.
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 system is trying to control the engine's braking by adjusting a valve, but the position sensor isn't giving the right info, which means the engine can't slow down as it should when you release the throttle.
What the computer is actually seeing
The ECM expects to see a position signal from the retarder valve sensor that corresponds with a specified range; typically, it should read between 0.5V (fully closed) and 4.5V (fully open).
What a healthy reading looks like
Voltage from the valve position sensor should be between 0.5V and 4.5V depending on the position; resistance should read around 10-40 ohms at the connector when the system is off.
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. Inspect wiring and connectors to the Engine Retarder Control Valve for damage or corrosion. If damaged, repair or replace as needed. Decision point: Is wiring intact? Yes: go to step 2. No: repair wiring and retest.
- 22. Measure the voltage at the retarder valve sensor connector with the key on and engine off. Expected voltage is between 0.5V and 4.5V. Decision point: Is voltage within range? Yes: go to step 3. No: replace sensor or check circuit continuity to the ECM.
- 33. With the engine running, command the retarder valve via the diagnostic tool and watch for actual valve position response. Decision point: Does the valve respond correctly? Yes: retest system for codes. No: replace the Engine Retarder Control Valve.
Common causes
- Damaged wiring or connector to the valve position sensor
- Faulty engine retarder control valve
- Failed position sensor
- ECM software issue
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code active?
It is moderately safe to drive, but performance will be affected, especially in braking situations.
Will this problem come back after repairs?
If the root cause is properly addressed, such as fixing wiring or replacing the valve, it should not return.
Why does this code sometimes pair with SPN 1595?
SPN 1595 is related to the same system and indicates a problem with the retarder valve itself, which can trigger SPN 1594.
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