P0898: Transmission Control System MIL Request Circuit Low

What it means

Voltage on the transmission control system MIL request circuit is below the expected window. Wire shorted to ground or driver low.

At a glance

• Usually lights the check-engine light

How it works

The transmission control system sends a malfunction-indicator-lamp request over a dedicated circuit so the vehicle can turn on the appropriate warning lamp. P0898 sets when the circuit voltage is too low, which can result from a short to ground, a poor connection, or a fault in the module's output circuit.

Common causes

Most likely first.

1. Fault in the MIL request circuit wiring
2. Poor electrical connection
3. Transmission control module circuit fault

Symptoms

• Check-engine or transmission warning light may not respond as expected

How to diagnose it

1. Scan all modules for related communication, lamp-request, and transmission codes, and note whether the warning lamps respond when faults are present.
2. Inspect the MIL request circuit wiring and connectors between the TCM and the receiving module for shorts to ground, damage, or loose terminals.
3. Check the relevant grounds and connector pins for corrosion or poor contact.
4. With a wiring diagram and scan tool, compare the TCM lamp-request command with circuit voltage and the receiving module's reported status.
5. If the circuit wiring and connections pass, test the TCM output and receiving-module input against the manufacturer's specification.

Common fixes

• Repair a MIL request wire shorted to ground.
• Clean, secure, or replace a poor connection in the request circuit.
• Repair damaged wiring between the TCM and the receiving module.
• Repair or replace a module only after its input or output circuit fault is confirmed.

Can I keep driving?

The fault may prevent the check-engine or transmission warning lamp from responding correctly, so do not rely on those lamps to alert you to a new fault. If shifting is abnormal, limit driving and stop if the vehicle loses drive.