Error Code P0885 is defined as TCM power relay control circuit/open. This is a generic trouble code, meaning it applies to all vehicles with the OBD-II system, especially those made since 1996 up to the present. This includes vehicles from, but not limited to, Chrysler, Dodge, Ford, Hyundai, Kia, Jeep, and Smart. However, it seems to be more common among Honda vehicles.
Suppose a vehicle stores Error Code P0885 with Malfunction Indicator Lamp (MIL) lit up. In that case, that means the Powertrain Control Module (PCM) has determined an open voltage, or there’s an unspecified condition in the TCM power relay control circuit.
While some TCM in OBD-II equipped modules are built into the PCM, most are stand-alone components. Depending on the vehicle make and model, codes that start with P, B, and U are related to TCM. For this error code, there’s a strong chance there are other related PCM or TCM codes as well.
The Controller Area Network (CAN) is a sophisticated system of connectors and wirings that works by transmitting data between the PCM and TCM. The data (including stored codes) may also be shared with other controllers through CAN. RPM (transmission input and output speed), wheel speed, and vehicle speed are shared between multiple controllers. They’re used to compare electronic control systems, anti-lock braking systems, and electronic stability control systems. This code is unique as it’s usually only stored if there are other traction control system related codes. An electronic or mechanical problem may cause these codes.
Control modules are a network of computers that controls the electronic transmission control system in OBD-II equipped vehicles. This includes constant communication between different control modules through the CAN.
The PCM utilizes input signals from multiple engine and transmission sensors to calculate automatic transmission shift strategy. A high-pressure pump (inside the transmission) forces fluid through the valve body and into the sprag assembly, in addition to lubricating and cooling the transmission. The high-pressure fluid allows the clutches to separate from the sprag momentarily so that the gear ratio may be changed smoothly. One or more electronic pressure control (EPC) solenoids help to regulate fluid pressure. Electronic pressure (EP) sensors provide the PCM with pertinent data regarding fluid pressure at various points in the transmission. Electronic shift solenoids are used to interrupt the flow of high-pressure fluid so that the transmission shifts gears when commanded. The PCM uses voltage input signals from the transmission input speed sensor and transmission output speed sensor to determine if the transmission is shifting efficiently.
If the PCM sees a problem that demands the illumination of the Check Engine light, this code will be stored.
- Disabled electronic traction control
- Limp-in mode – transmission unable to shift out of low gear
- Transmission unable to shift
- Erratic shift pattern in the transmission
- Disabled ABS
- Blown fuse or bad relay (fusible link)
- Open or shorted CAN circuits
- Defective vehicle speed sensor
- Failed mechanical transmission
- Defective PCM
- Defective TCM
- Programming error
How to Check
As with most codes, you need a diagnostic scanner, DVOM (digital volt/ohmmeter), and a reliable vehicle information source that shows how to diagnose the code. An oscilloscope can also help in diagnosing various speed sensors.
You can save time by looking for a TSB (technical service bulletin) that shows similar error code, year, make and model, engine, and symptoms. You may find this info in a vehicle information source.
First, you need to retrieve all the stored codes and the pertinent freeze frame data by connecting the scanner to the diagnostic port of the vehicle. Then, make sure you clear the codes before taking the vehicle for a test drive. One of two things must occur in your test drive; the error code restored, or the PCM enters readiness mode.
The problem is intermittent if the PCM enters readiness mode. This means you may need to wait for the problem to worsen before you can diagnose it accurately. If the code is restored, then you can proceed with your diagnosis.
Use your vehicle information source for the diagnostic flow chart, face views, component locator charts, connector pinout charts, and wirings diagram.
Next, inspect all related connectors and wirings. Replace or repair any damaged components.
Then, test the voltage and ground circuits of TCM and PCM using the DVOM. Also, check the system fuses. Replace any blown or defective fuses, retest as needed.
If there are both voltage and ground at the TCM, test the corresponding circuit at the PCM connector. No voltage means there’s an open circuit between the PCM and the component in question. If there is voltage, you can suspect a programming error or a defective PCM or TCM.
How to Fix
- Replacement of damaged or faulty connectors, components, and wires
- Replacement of CAN bus harness wiring or whole harness
- Replacement of faulty control modules, including TCM
The transmission may start to shift harshly when this code is stored.
If the vehicle shows this code, it must be addressed as soon as possible. And since traction control is in problem, it is important to avoid wet, slippery, or rugged surfaces.
This code is usually stored due to a defective contact relay.