Transmission Control System MIL Request Circuit High
Code P0899 indicates that the transmission control module (TCM) has detected a high voltage condition in the malfunction indicator lamp (MIL) request circuit. This circuit is used by the TCM to request the powertrain control module (PCM) to illuminate the check engine light. A high voltage reading suggests a short to power, open circuit, or faulty component in the wiring or connectors between the TCM and PCM.
1. Symptoms You Will Notice
- Check engine light illuminated
- Transmission may operate in limp mode or have harsh shifts
- Possible transmission performance issues
2. Most Common Causes
- Short to voltage in the MIL request circuit wiring
- Faulty transmission control module (TCM)
- Damaged or corroded connectors in the circuit
- Open circuit in the MIL request wire
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to retrieve all stored codes and freeze frame data.
Step 2: Inspect the wiring and connectors for the MIL request circuit for damage, corrosion, or shorts.
Step 3: Test the circuit voltage with a multimeter to confirm high voltage condition.
Step 4: Check for TCM software updates or replace TCM if necessary.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as the transmission may enter limp mode, causing reduced performance and potential damage.
How much does it cost to fix?▼
Repair costs typically range from $50 to $150 for wiring repairs or connector replacement, but TCM replacement can be more expensive.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.