🚨 Diagnostic Profile
Vehicle Make: Chevrolet (CHEVY)
Description: TCM Power Control Relay Circuit Open. The transmission control module (TCM) power control relay circuit is reporting an open condition, which can interrupt power or control to the TCM.
🚨 Repair Difficulty Tier
Tier: [Intermediate]
This repair requires working knowledge of relay control circuits, back-probing connectors, and reading wiring diagrams. Access to the relay and TCM connectors may require partial trim or component removal depending on the model year.
🛠️ Resolution Steps
Step 1: Preliminary Inspection
- Scan all modules for DTCs and record freeze frame data before clearing anything.
- Verify battery state of charge and confirm battery voltage reads at least 12.4V at rest, with no excessive voltage drop at the battery terminals under cranking or key-on load.
- Locate the TCM power control relay in the underhood power distribution/relay center (consult the fuse box lid legend or service information for the exact cavity position, as location varies by platform and model year) and inspect the relay socket for corrosion, heat discoloration, or loose/spread terminals.
- Inspect the corresponding relay fuse in the same underhood power distribution center for an open circuit, bridging, or visible discoloration using a test light or multimeter continuity check.
- Inspect the TCM connector and harness (TCM is typically mounted on or near the transmission case, or integrated with the PCM depending on platform) for pushed-out, bent, or corroded terminals.
- Check main chassis and powertrain ground connections serving the TCM and power distribution circuit for corrosion or looseness, as a poor ground can mimic an open relay circuit condition.
Step 2: Diagnostic Verification
- Consult the OEM service information system (GM Techline / ACDelco TDS) for the correct model-year-specific wiring diagram covering the TCM power control relay, relay control circuit, and fused B+ feed circuits.
- With the ignition in the key-on, engine-off (KOEO) state, measure supply voltage at the relay feed (constant B+) and switched output terminals; both should read battery voltage (approximately 12-14V) with the key on and the relay energized.
- Measure relay coil control circuit voltage (should toggle between near 0V and battery voltage when commanded by the PCM/BCM driver) and check coil resistance with the relay removed and an ohmmeter, comparing readings against the relay manufacturer’s published coil resistance specification rather than an assumed fixed value.
- Perform a continuity test (should read near 0 ohms) on the suspected open circuit between the relay socket and TCM connector, with both ends disconnected and ignition off.
- Check for shorts to voltage or ground on the same circuit using a multimeter with the circuit isolated and key off.
- Confirm the fault by reproducing the DTC after repair or by monitoring live TCM data (ignition voltage, TCM power relay status PID if available) during key-on and engine-running states.
Step 3: Resolution & Reset Process
- If the relay fails coil resistance or contact continuity/load tests, replace it with an OEM or OE-equivalent quality relay of the correct part number and amperage rating.
- If the harness shows an open or high resistance, repair the circuit using proper solder and adhesive-lined heat shrink techniques (avoid simple crimp-only butt connectors in high-vibration powertrain areas).
- Replace any damaged TCM connector terminals or blown fuses using OEM-specified terminals and fuse amperage ratings only — never substitute a higher amperage fuse.
- Clear DTCs with a scan tool capable of bidirectional GM controls, then perform any TCM power-on reset, ignition cycle relearn, or module reprogramming/configuration procedure called for in service information if the TCM lost calibration due to the power interruption.
- Road test the vehicle through all transmission operating ranges and shift conditions, then recheck for pending or history codes before releasing the vehicle.
📦 Parts, Labor, and Budget Estimates
Required Components/Software:
- TCM power control relay (OEM ACDelco or equivalent micro/ISO relay) — verify exact GM part number against VIN
- Relay circuit fuse, if damaged — match OEM amperage rating exactly
- Connector terminals, pigtail, or harness repair kit, if corrosion or damage is found at the TCM or relay connector
- GM-compatible scan tool with bidirectional control and TCM reset/relearn capability (GM MDI2/Techline Connect, or capable aftermarket tool such as Autel/Snap-on with GM software)
Average Component Price: Relay: $15–$45; Fuse: $5–$15; Connector/terminal repair kit: $20–$75; TCM assembly (only if internally faulted, uncommon for this code): $250–$650 part cost
Estimated Labor Hours: Diagnostic time: 0.8–1.5 hours; Relay/fuse replacement: 0.3–0.5 hours; Harness or connector repair: 0.8–2.0 hours depending on access; TCM replacement/reprogramming (if required): 1.5–3.0 hours. Total shop estimate typically ranges $150–$450 for relay/fuse-level repairs, or $450–$900+ if TCM replacement and programming are required.