What Does P0899 Mean?
The TCM has detected a high voltage condition on the circuit used to request illumination of the malfunction indicator lamp (MIL). This indicates the MIL request line is shorted to a voltage source, which may cause the check engine light to remain on continuously regardless of actual fault status, or it may disrupt communication between the TCM and instrument cluster.
Common Causes
30%
Short to battery voltage in the MIL request circuit wiring
25%
Faulty TCM with internally shorted MIL request output driver
20%
Corroded or water-damaged connector causing voltage feedback on the MIL circuit
15%
Instrument cluster fault pulling the MIL line high
10%
Wiring harness routed too close to a high-voltage source causing induction or contact
Diagnostic Steps
1
Check if the MIL is stuck on; a continuously illuminated check engine light with no other stored codes can confirm a shorted-high MIL request line.
2
Disconnect the TCM connector and measure voltage on the MIL request circuit; if voltage is still present, the short is in the wiring or instrument cluster side.
3
Inspect the MIL request circuit wiring harness for chafing against sharp edges or contact with other high-voltage wires.
4
Check the instrument cluster connector for corrosion, water intrusion, or bent pins that could create a short.
5
If the wiring is clean and the fault remains with the instrument cluster disconnected, the TCM MIL driver is likely shorted internally.
Estimated Repair Cost
$150 - $500
Parts + labor, varies by vehicle and location
The TCM has detected a high voltage condition on the circuit used to request illumination of the malfunction indicator lamp (MIL). This indicates the MIL request line is shorted to a voltage source, which may cause the check engine light to remain on continuously regardless of actual fault status, o...
The most common cause of P0899 (Transmission Control System MIL Request Circuit High) is: Short to battery voltage in the MIL request circuit wiring
Typical repair costs for P0899 range from $150 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A stuck-high MIL circuit can mask real warning light requests or cause the driver to ignore a continuously lit MIL, leading to missed warnings for genuine transmission or engine faults.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0899 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Powertrain
System
Transmission
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
