Code P0885: Definition, Symptoms, Causes and Diagnosis
📌 Quick Overview
- Definition: Electrical problem in the TCM (Transmission Control Module) power relay circuit.
- Severity: Medium to High (risk of transmission damage).
- Symptoms: Harsh gear shifts, ABS/traction control system deactivated, associated codes.
- Common Causes: Blown fuse, faulty relay, damaged wiring, TCM/PCM failure.
1. Meaning of Code P0885
Code P0885 indicates that the PCM (Powertrain Control Module) has detected an electrical anomaly in the TCM power relay circuit. This relay controls the electrical power supply to the TCM, which is essential for managing the automatic transmission.
Key Operation:
- The TCM communicates with the PCM via the CAN (Controller Area Network) bus.
- Shared data includes: engine RPM, vehicle speed, hydraulic pressure.
- A failure in this circuit disrupts the shift strategy and related systems (ABS, stability control).
2. Severity and Risks
- Immediate Problems:
- Harsh or impossible gear changes.
- Deactivation of safety systems (ABS, traction control).
- Long-Term Risks:
- Premature wear of clutches and hydraulic components.
- Transmission overheating.
3. Common Symptoms
- 🚨 Check Engine Light illuminated (MIL).
- 🔧 Erratic or delayed gear changes.
- 🛑 Automatic deactivation of traction control/ABS.
- ⚡ Other stored codes (e.g., P0865, U codes related to CAN).
4. Possible Causes
| Category | Detailed Causes |
|---|---|
| Electrical | – Blown fuse or faulty TCM relay. |
| – Damaged wiring (short circuits, chafed wires). | |
| – Oxidized or poorly secured connectors. | |
| Electronic | – TCM or PCM failure. |
| – Module programming error. | |
| Mechanical | – Hydraulic pressure problem in the transmission. |
| CAN System | – Disturbances or failures in the communication network. |
5. Diagnostic Steps
Required Tools:
- OBD-II scanner (reading codes and live data).
- Digital multimeter (testing voltage/resistance).
- Oscilloscope (analyzing speed sensor signals).
Procedure:
- Code Reading:
- Identify all stored codes (P, B, U).
- Consult Technical Service Bulletins (TSBs) for known solutions.
- Visual Inspection:
- Check fuses, relays, and wiring related to the TCM.
- Look for signs of burning, corrosion, or cut wires.
- Electrical Tests:
- Measure the TCM power supply voltage (should be ~12V).
- Test the continuity of the CAN circuits between TCM and PCM.
- Component Verification:
- Replace the TCM relay with a known good relay for testing.
- Use the oscilloscope to analyze speed sensor signals.
- Advanced Diagnostics:
- If the TCM/PCM is suspected, perform a test with a replacement module.
- Update module software if programming errors are detected.
6. Common Solutions
- 🔌 Replace a faulty fuse/relay: Average cost €10–50.
- 🔧 Repair damaged wiring: Solder or replace problematic wires.
- 💻 Reset/Update the TCM/PCM: Requires a professional diagnostic tool.
- ⚠️ Replace the TCM: High cost (€300–1000 depending on model).
7. Practical Tips
- Do not ignore intermittent codes: An intermittent P0885 can signal an emerging problem.
- Check the transmission fluid level and condition: Low hydraulic pressure can worsen symptoms.
- Consult a professional: CAN and TCM systems require expertise for accurate diagnosis.
8. Frequently Affected Models
- Hyundai/Kia: Tucson, Sportage (recurring relay issues).
- Jeep/Dodge: Grand Cherokee, Ram 1500 (TCM failures).
- Ford: Focus, F-150 (fragile wiring near the transmission).
Conclusion
Code P0885 signals a critical electrical problem affecting transmission management. A methodical diagnosis (fuses, relays, wiring) is essential to avoid costly repairs. If technical skills are lacking, entrust the vehicle to a specialist in automotive electronic systems.
⚠️ Reminder: A malfunctioning transmission can endanger your safety. Act quickly!