Transmission 4-Wheel Drive Low Indicator Short Circuit To Ground
The transmission's 4-wheel drive low indicator circuit is shorted to ground, like a light switch stuck in the on position with a broken wire. The ECU can't properly control or read the 4WD low signal because the electrical path is compromised.
The ECM monitors the voltage signal from the 4WD low indicator circuit, expecting a normal high voltage when inactive and low voltage when engaged. A short to ground forces the signal to remain at 0V, preventing the ECU from distinguishing between active and inactive states. This triggers the fault when the circuit voltage remains abnormally low.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| 4WD Low Indicator Voltage | 4.5-5.0V (inactive), 0.5-1.0V (active) | Below 0.3V continuously or shorted state |
| Circuit Resistance | 100+ kΩ to ground (open) | Below 10Ω (short to ground) |
Code P1816 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P1816 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.