P0887 Code: TCM Power Relay Control Circuit High
The circuit that switches the transmission power relay reads high voltage when it shouldn't.
Unverified: this manufacturer-specific definition comes from a single source or varies by model. Confirm it with a brand-specific scan tool.
At a glance
Severity: Moderate
- Meaning
- TCM Power Relay Control Circuit High
- System
- Transmission · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $20–$1,300
- DIY difficulty
- Moderate
On many vehicles, the transmission computer (or the engine computer) switches a relay that feeds battery power to the TCM's outputs – on Chrysler products this is often called the transmission control relay, and it powers the solenoid pack. P0887 means the control side of that relay reads a higher voltage than expected, which usually points to a short to battery voltage on the control wire, a relay with a shorted coil, the wrong relay installed, or a driver inside the module that can't pull the circuit down. Without a properly controlled relay the solenoids may lose power, so the transmission sits in its default gear. Wording varies between manufacturers – some service literature describes related faults in terms of the relay 'sense' circuit – so the factory definition for your vehicle should be checked.
Can I keep driving? Usually drivable in the default gear, with poor acceleration and high rpm at speed. If the relay stays on after you switch off, the battery can drain overnight, so pull the relay or have it fixed promptly.
How to read P0887
- P Powertrain
- 0 Generic (SAE)
- 8 Transmission
- 87 Specific fault
Symptoms
- Transmission stuck in one gear from the moment the engine starts
- Relay clicking rapidly or not clicking at all at key-on
- Battery drained after the car sits overnight
- Other solenoid or voltage codes stored at the same time
- Fault started after a relay or fuse box was replaced or got wet
- Transmission warning, with the check engine light on some models
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Relay control wire shorted to battery voltage
- Faulty relay (shorted coil or internal fault)
- Wrong or non-matching relay installed
- Water or corrosion in the fuse/relay box
- TCM or PCM relay driver failure
- Damaged power distribution center terminal
Diagnosis step by step
Identify the relay and its wiring
Use the wiring diagram to find the transmission power relay, which module controls it, and whether the module switches the ground side or the power side of the coil. That determines what 'high' means on your vehicle.
Tools: OBD-II scanner
Swap in a known-good identical relay
Replace the relay with an identical one – same part number and pin layout, including any internal diode or resistor. If the code doesn't return after clearing, the old relay was the problem.
Tools: Pliers
Measure the relay coil
Measure resistance across the relay's coil terminals; typical automotive relays read roughly 50–120 ohms. A very low reading indicates a shorted coil that can overload the module driver.
Tools: Multimeter
Check the control wire for a short to voltage
With the relay removed, the module unplugged and the key on, measure voltage on the control wire at the relay socket. It should read 0 V; any voltage means the wire is shorted to a power circuit somewhere in the harness.
Tools: Multimeter
Inspect the relay box
Look for water, green corrosion or melted plastic in the fuse and relay box, and check terminal tension at the relay socket. Water ingress from a blocked drain or cowl leak is a common cause of control-circuit faults.
Tools: Flashlight, Screwdriver
Test the module driver
With wiring and relay good, command the relay from the scan tool and watch the control wire. If it doesn't switch as specified, the TCM or PCM driver is at fault and the module needs replacing and programming.
Tools: OBD-II scanner, Multimeter
Where the parts are
- 1Battery
- 2Alternator
- 3Engine computer (ECM)
- 4CAN bus
- 5Transmission
- 6Wheel speed sensor
- 7High-voltage battery
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Replace transmission power relay | Yes | $20–$120 |
| Repair shorted control wire | No | $120–$400 |
| Clean or repair fuse/relay box terminals | No | $100–$350 |
| Replace power distribution module or fuse box | No | $400–$1,200 |
| Replace and program TCM or PCM | No | $500–$1,300 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Dodge
Many Dodge vehicles route transmission solenoid power through a transmission control relay in the under-hood power distribution module. Relay and power distribution module terminals are common trouble spots, so they're checked before the TCM.
Field data
| Jeep | 12 | Cherokee |
|---|
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Depends
Whether P0887 lights the check engine lamp varies by manufacturer. If it does, the vehicle fails an OBD smog or emissions test; if only a transmission message appears, the test result depends on the station's check of stored codes and monitors.
Frequently asked questions
What does the TCM power relay do?
It switches battery power to the transmission's solenoids and, on some vehicles, to the TCM itself. The computer turns the relay on at key-on and off after shutdown.
Can I just replace the relay?
Swapping in an identical relay is a cheap first test and often fixes it. If the code returns, the control wire, fuse box or module driver needs to be tested.
Why is my battery dying with P0887?
If the control circuit is shorted so the relay stays energized after the engine is off, it keeps drawing current. That's a sign of a short to voltage in the control wire or a failing relay.
Is P0887 the same as a relay sense code?
Not exactly. The control circuit is what the module uses to switch the relay; the sense circuit reports back whether the relay output is actually powered. Manufacturers sometimes word them differently, so check your vehicle's factory definition.