P1315

Kickdown Relay Hold Circuit Fault

Powertrain Transmission Control Kickdown Control 🟡 Moderate — Fix within a week ⚠️ Drive with Care
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What This Actually Means

In plain language — no jargon

The kickdown relay, which helps the transmission downshift for acceleration, isn't holding its electrical circuit properly. Think of it like a switch that's supposed to stay latched but keeps popping open.

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Symptoms You May Notice

3 known symptoms for this code
Transmission won't downshift when accelerating hard
No engine braking when coasting
Check engine light illuminated
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECM monitors the kickdown relay coil voltage and continuity after commanding it closed. It detects if the relay fails to maintain electrical connection or if circuit resistance exceeds normal parameters, indicating a stuck, burned, or faulty relay.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Relay Coil Voltage 11-14V when energized Below 9V or erratic dropout
Circuit Resistance Less than 5 ohms Greater than 10 ohms or open circuit
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Kickdown relay
Locate relay in engine bay fuse/relay box, note its position, pull straight out and insert new relay.
2
Relay socket and wiring harness
Inspect socket for corrosion, burnt contacts, or loose pins; clean with contact cleaner or replace socket if damaged.
3
Transmission control module connector
Check TCM connector pins for corrosion or looseness and reseat firmly to restore signal integrity.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code P1315 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 P1315

What happens after you fix the fault

Once the fault is repaired, P1315 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.