P0887 – TCM Power Relay Control Circuit High

System: Powertrain | Standard: ISO/SAE Controlled | Fault type: Circuit High

Definition source: SAE J2012/J2012DA (industry standard)

DTC P0887 indicates the control circuit for the TCM power relay is being detected as “high” by the control module logic. In practical terms, the module is seeing an unexpectedly high electrical signal on the relay control circuit when it expects the circuit to be pulled low or otherwise change state. This is a circuit-high electrical fault, not a confirmed relay or module failure by itself. The exact relay strategy, pinout, and how the monitor runs vary by vehicle, so always verify circuit function, connector views, and test conditions in the correct service information before replacing parts. Treat this as an electrical diagnosis: confirm the high signal, then isolate whether it is caused by wiring, the relay/driver path, or power/ground issues.

What Does P0887 Mean?

P0887 – TCM Power Relay Control Circuit High means the powertrain control system has detected a high electrical condition on the transmission control module (TCM) power relay control circuit. SAE J2012 defines the standardized structure and naming of DTCs, and for this code the reported fault type is “Circuit High,” which points to an electrical signal that is higher than expected for the commanded or monitored state. Depending on the vehicle’s design, the control circuit may be actively driven by a module (low-side or high-side control) and may be monitored for feedback; the DTC sets when the observed circuit state does not match what should be present during the monitor’s enable conditions.

Quick Reference

• Subsystem: TCM power relay control circuit (relay command/driver and any related feedback/monitoring path, varies by vehicle).
• Common triggers: Short-to-power on the control wire, open ground on a low-side controlled circuit, backfeed from another circuit, relay control driver stuck high, or a connector condition that leaves the line biased high.
• Likely root-cause buckets: Wiring/connector faults; relay/control circuit backfeed; power/ground integrity issues; module driver or internal fault; rarely calibration/logic issues (verify prerequisites first).
• Severity: Potentially high; can affect TCM power-up, shifting behavior, and may cause fail-safe operation, reduced performance, or a no-shift/no-start condition depending on strategy.
• First checks: Confirm battery/charging health, inspect relay and related fuses, inspect harness routing near heat/movement points, and check for obvious connector damage/corrosion or loose pins.
• Common mistakes: Replacing the relay or control module without proving the circuit-high condition, skipping power/ground checks, and not checking for backfeed from aftermarket wiring or adjacent circuits.

Theory of Operation

The TCM power relay is used to switch a clean, controlled supply to the TCM and sometimes related transmission components. A control module commands the relay on and off through a relay control circuit. Depending on design, the module may switch the relay using a low-side driver (pulling the control line toward ground) or a high-side driver (pulling it toward power). Many systems also monitor the control circuit (and sometimes relay output) to ensure the command and electrical response agree.

P0887 sets when the relay control circuit is detected at an unexpectedly high electrical level for the current command/state. Typical electrical reasons include a short-to-power, an open in the expected pull-down/ground path on low-side control, or a backfed voltage from a related circuit that keeps the control line high. The monitor logic, enable conditions, and exact circuit layout vary by vehicle and must be confirmed in service information.

Symptoms

• Warning light: Check engine light or powertrain warning illuminated.
• Fail-safe shifting: Harsh shifts, limited gear operation, or default gear strategy.
• No/erratic shifting: Delayed engagement, intermittent shift response, or inability to change gears.
• Intermittent operation: Symptoms that appear with vibration, heat, or after hitting bumps (wiring sensitivity).
• Reduced performance: Limited acceleration or reduced power behavior tied to transmission protection logic.
• No-start/no-crank: Possible on some designs if relay logic affects powertrain interlocks (varies by vehicle).
• Electrical anomalies: Multiple related electrical DTCs due to shared power/ground or backfeed conditions.

Common Causes

• Short-to-power on the TCM power relay control circuit (harness contact to a battery feed, backfeed from another circuit, or insulation damage)
• Open or high-resistance ground on the relay control side (including poor ground splice integrity), allowing the control line to stay pulled high
• Relay control circuit open between the module driver and the relay coil/control terminal, causing the monitored line to remain high
• Connector faults at the relay, module, fuse/relay box, or intermediate junctions (corrosion, spread terminals, poor pin fit, water intrusion, or partial disengagement)
• Incorrect relay installed or relay with an internal fault that causes abnormal feedback/high signal on the control/monitor circuit
• Power feed backfeeding into the control/monitor circuit due to wiring misrouting, prior repairs, or aftermarket electrical additions (varies by vehicle)
• Fault in the module driver or monitoring circuitry (the control output is stuck high or the feedback sense circuit is biased high)
• Faulty fuse/relay box internal bus or damaged internal traces causing unintended power on the control circuit (varies by vehicle design)

Diagnosis Steps

Tools you’ll typically need include a scan tool capable of reading freeze-frame and live data (and commanding outputs if supported), a digital multimeter, a test light appropriate for automotive circuits, and back-probing leads. A wiring diagram and connector pinout from service information are essential. For intermittent issues, use a harness wiggle tool approach and scan tool data logging.

1. Confirm the code and capture context: Verify P0887 is current or pending. Record freeze-frame data, battery voltage status (as reported), and any related transmission/power supply DTCs. Clear codes and see if P0887 returns immediately or only after a drive cycle.
2. Check for related power/ground concerns first: Inspect for any DTCs indicating system voltage issues or module power supply faults. If multiple modules show power-related codes, address primary power/ground distribution concerns before focusing narrowly on the relay control circuit.
3. Perform a visual inspection of the relay circuit path: With ignition off, inspect the power relay, relay socket, fuse/relay box area, and visible harness routing. Look for damaged insulation, signs of overheating, loose terminals, corrosion, or moisture. Do not skip checking for prior wiring repairs or non-factory splices (varies by vehicle).
4. Identify the relay and circuit roles using service information: Using the wiring diagram, identify which relay is the TCM power relay, which terminal is the coil/control side, which is the load side, and whether the control is high-side or low-side switched (varies by vehicle). This prevents testing the wrong circuit or misinterpreting a “high” reading.
5. Key-off circuit bias check (unplug-and-observe): With ignition off, disconnect the relay and measure the control circuit at the relay socket using the diagram reference. A circuit that reads “high” when it should not be driven may indicate a short-to-power, backfeed, or a stuck module driver. If unplugging the module-side connector causes the “high” to disappear, suspect backfeed through the module or harness segment near the module.
6. Check for short-to-power/backfeed: If the control circuit shows a high condition when it should be inactive, isolate the harness by disconnecting intermediate connectors/junctions (per service info) to narrow down where power is entering the control line. Pay attention to areas where the harness passes near sharp brackets, hot components, or shared conduit with power feeds.
7. Verify ground integrity with voltage-drop testing: When the circuit is commanded on (or during the condition when the monitor runs), perform voltage-drop tests across the relevant grounds (battery negative to module ground, and battery negative to relay/coil ground path, as applicable). Excessive drop indicates ground resistance that can bias a monitored line high, depending on circuit design.
8. Relay evaluation (bench and in-circuit): Confirm the relay part is correct and that the relay is not internally shorted in a way that could feed voltage into the control/monitor circuit. If service info provides an output command test, command the relay on/off while observing live data and measuring at the relay socket to confirm the control line responds appropriately.
9. Wiggle test with live-data logging: With the scan tool logging relevant parameters (relay command status if available, module supply status, and DTC status), wiggle the harness at the relay/fuse box, along the harness run, and at the module connector. If the control circuit spikes high or the code resets during movement, focus on connector pin fit, terminal tension, and hidden breaks under insulation.
10. Connector pin-fit and terminal tension checks: If an intermittent is indicated, inspect connectors for spread terminals, backing-out pins, and corrosion. Verify proper terminal tension using appropriate methods (per service info). Repair or replace terminals as needed, then re-check for a stable control signal under the same conditions that previously triggered the fault.
11. Module driver/monitoring assessment: If the wiring, relay, and power/grounds test good and the control circuit still remains high (or reports high) under controlled conditions, suspect an internal module driver or sense circuit fault. Before replacement, re-verify all powers/grounds to the module under load with voltage-drop testing and confirm no harness backfeed paths remain.

Professional tip: A “circuit high” fault on a relay control line is often caused by unintended power being introduced into the control/monitor circuit (backfeed/short-to-power) rather than the relay itself. Use systematic isolation: disconnect the relay, then isolate harness segments and connectors one at a time while monitoring the control line and scan tool data logging to pinpoint exactly where the high condition is being introduced.

Possible Fixes & Repair Costs

Repair costs for P0887 can vary widely because the fix depends on what’s actually driving the TCM power relay control circuit high—wiring condition, connector integrity, relay type, and labor time to access and test the circuit.

• Repair wiring faults: Locate and correct short-to-power conditions, damaged insulation, rubbed-through harness sections, or incorrect splices affecting the relay control circuit.
• Restore ground integrity: Clean/tighten ground points and repair broken ground wires that can make the control circuit read high due to a missing return path (varies by vehicle design).
• Service connectors: Reseat connectors, correct pin fit issues, remove corrosion, and repair terminal tension problems at the relay, fuse/relay block, or module connectors.
• Replace the power relay: If testing confirms the relay is sticking, internally shorted, or otherwise not behaving correctly, replace the relay with the correct type for the application.
• Repair fuse/relay block faults: Address overheated cavities, loose terminals, or internal bus issues that can backfeed power into the control circuit and keep it high.
• Correct aftermarket wiring: Remove or rework non-factory power feeds, remote-start/alarm wiring, or accessory taps that can unintentionally energize or backfeed the relay control circuit.
• Module-level repair: If circuit integrity is verified and the control output still remains high, module output driver fault or calibration issues may be considered per service information and confirmed test results.

Can I Still Drive With P0887?

Driving with P0887 is risk-dependent because a TCM power relay control circuit high condition can disrupt transmission control, potentially causing harsh shifting, a failsafe mode, reduced performance, or even a no-start or stall depending on how the power relay is used. If you notice stalling, no-start, sudden loss of shifting control, reduced power, or warning indicators related to powertrain control, do not continue driving—have the vehicle inspected and repaired. If the vehicle still drives normally, limit driving, avoid heavy loads, and prioritize diagnosis soon.

What Happens If You Ignore P0887?

If ignored, P0887 may lead to intermittent or worsening transmission control issues, repeated limp-in operation, increased stress on drivetrain components from abnormal shifting, and potential breakdown if the control circuit fault becomes persistent. Electrical backfeed or wiring damage that causes a circuit-high condition can also spread to adjacent circuits, creating additional faults and making later diagnosis more complex.

Related Relay Tcm Codes

Compare nearby relay tcm trouble codes with similar definitions, fault patterns, and diagnostic paths.

• P0891 – TCM Power Relay Sense Circuit High
• P0690 – ECM/PCM Power Relay Sense Circuit High
• P0866 – TCM Communication Circuit High
• P0890 – TCM Power Relay Sense Circuit Low
• P0888 – TCM Power Relay Sense Circuit
• P0886 – TCM Power Relay Control Circuit Low

Key Takeaways

• P0887 indicates a circuit-high condition in the TCM power relay control circuit, typically caused by short-to-power, backfeed, or missing ground on the control side.
• Don’t replace parts first; verify the control circuit state, connector integrity, and power/ground paths with test-driven checks.
• Wiring and connector issues are common, especially near fuse/relay blocks, harness routing points, and areas with heat or vibration.
• Relay and fuse/relay block faults are possible, but should be confirmed by inspection and electrical testing.
• Module faults are last and should only be considered after the circuit is proven healthy and free of backfeed or ground issues.

Vehicles Commonly Affected by P0887

• Vehicles with externally switched TCM power relays controlled by a module driver circuit.
• Vehicles with integrated power distribution modules that combine relay logic and fusing in a single assembly.
• Applications with multiple control modules sharing power feeds where backfeed between circuits is possible.
• Vehicles exposed to moisture, road salt, or heat that can accelerate terminal corrosion and fuse/relay block damage.
• High-mileage vehicles with harness insulation wear and repeated vibration near brackets or sharp edges.
• Vehicles with recent electrical work such as battery replacement, fuse/relay service, or harness repairs that may introduce pin-fit or routing issues.
• Vehicles with added electrical accessories that tap ignition or relay circuits and can create unintended power paths.
• Vehicles with underhood fuse/relay boxes located in high-heat areas where terminal tension and plastic housings can degrade over time.

FAQ

Is P0887 usually a bad relay or a wiring problem?

P0887 is more accurately treated as an electrical “circuit high” problem than a confirmed relay failure. A relay can be the cause, but common culprits include short-to-power in the control wire, backfeed through damaged fuse/relay block terminals, or a ground/return issue that leaves the control circuit reading high. Testing should decide the direction of the repair.

What does “circuit high” mean for the TCM power relay control circuit?

“Circuit high” means the control circuit is being seen at an abnormally high electrical state relative to what the module expects during its self-checks. This often points to short-to-power, unintended backfeed from another powered circuit, or an open/failed ground path on the control side (design varies by vehicle). It does not, by itself, prove a specific component has failed.

Can a weak battery cause P0887?

A weak battery is more commonly associated with low-voltage and reset-type complaints, but it can contribute indirectly if it leads to unstable module operation or abnormal relay control behavior during cranking. However, P0887 specifically indicates a circuit-high condition, so focus on finding why the relay control circuit is being held high or backfed rather than assuming low battery voltage is the root cause.

Will clearing the code fix P0887?

Clearing P0887 only erases stored fault information; it does not correct the underlying electrical condition. If the circuit high condition is still present, the code will typically reset when the monitor runs again. Clear the code after repairs or to confirm whether the fault is intermittent, then retest under the conditions that originally set it.

What should I inspect first for P0887?

Start with the fuse/relay box area: verify the correct relay is installed, inspect for heat damage, loose terminals, corrosion, and signs of backfeed. Then inspect the relay control wire routing for chafing or contact with powered circuits, and confirm grounds are clean and secure. If available, use scan data to see commanded relay state versus actual circuit behavior, and verify findings with electrical tests.

For a reliable repair, confirm P0887 is resolved by rechecking relay control behavior after repairs and completing an appropriate road test or functional test per service information.