P0887

TCM Power Relay Control Circuit High

Powertrain Transmission Control TCM Power Relay Circuit 🟡 Moderate — Fix within a week ⚠️ Drive with Care
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What This Actually Means

In plain language — no jargon

The transmission control module's power relay isn't receiving the right electrical signal—it's stuck in a high voltage state instead of cycling normally. Think of it like a light switch that won't turn off, causing the relay to stay energized when it shouldn't.

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Symptoms You May Notice

3 known symptoms for this code
Transmission shifting delays or won't shift into certain gears
Check engine light illuminated with reduced power mode active
Vehicle may go into limp mode or failsafe transmission operation
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECM monitors the voltage signal on the TCM power relay control circuit. When the ECM commands the relay on/off, it expects voltage to drop to near ground when off and rise to battery voltage when on. A 'high' fault means the circuit voltage remains elevated when the relay should be de-energized.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Relay Control Voltage (OFF state) 0–0.5V >4.5V when command is OFF
Relay Control Voltage (ON state) 10–14V No voltage drop to ground
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Relay connector and wiring harness
Inspect the TCM power relay connector for corrosion, loose pins, or damaged wires and clean or reseat connections.
2
TCM power relay
Replace the relay itself if it's stuck in the ON position or has internal resistance preventing proper de-energization.
3
TCM control module
If wiring and relay are good, the TCM output driver circuit may be faulty and require module replacement or reprogramming.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code P0887 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.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.
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How to Clear Code P0887

What happens after you fix the fault

Once the fault is repaired, P0887 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.

✅ Safe to Clear When
  • Fault has been diagnosed and repaired
  • You want to confirm the repair worked
  • Code appeared after a sensor was cleaned
⚠️ Do Not Clear When
  • Preparing for an emissions/PUC test
  • Root cause is still undiagnosed
  • Check engine light is flashing
Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.