DTC Advanced Diagnostics: P154D (2.0L Engine)
DTC P154D: Powertrain Control Module (PCM) Low Voltage at Engine Auto Restart
General Description
A power supply to each electrical unit temporarily drops due to the drop of the 12 volt battery voltage when the engine is restarted (starter is running) from auto idle stop condition. Normally, the voltage does not fall below the minimum level to operate the electrical unit. However, if there is a 12 volt battery performance deterioration or other abnormality to cause a low voltage, the voltage falls below the minimum level and causes an electrical unit reset. The powertrain control module (PCM) is able to monitor the minimum voltage level during engine restart from auto idle stop condition since the PCM is capable of operating at low voltage compared to other electrical unit. If the PCM power supply voltage is a specified voltage or less for a specified time, the PCM detects a malfunction and stores a DTC.
Monitor Execution, Sequence, Duration, DTC Type
| Execution | Continuous |
| Sequence | None |
| Duration | 0.01 second or more |
| DTC Type | Two drive cycles, MIL off |
Enable Conditions
| Condition | |
|---|---|
| Other | Engine cranking to restart from auto idle stop |
Malfunction Threshold
The PCM power supply voltage is less than 5.66 V for at least 2 times when the engine is restarted from auto idle stop condition.
Possible Cause
- 12 volt battery performance deterioration
- Use of non-genuine 12 volt battery
- Poor connections or loose terminals between body ground and 12 volt battery (-) terminal
- Poor or loose 12 volt battery (+) terminal cables and connections
- Addition of high electric load device
Confirmation Procedure
Operating Condition
- Start the engine. Hold the engine speed [Engine Speed] at 3, 000 rpm without load (in P or N) until the radiator fan comes on.
- Test-drive the vehicle under the auto idle stop system operating condition, and stop the engine using auto idle stop.
- Repeat Driving Pattern steps 1 through 3 at least 2 times.
- Drive the vehicle in this manner only if the traffic regulations and ambient conditions allow.
[ ]: HDS Parameter
Diagnosis Details
Conditions for setting the DTC
When a malfunction is detected during the first drive cycle, a Pending DTC is stored in the PCM memory. If the malfunction returns in the next (second) drive cycle, a Confirmed DTC and the freeze data are stored. The MIL does not come on.
Conditions for clearing the DTC
The Pending DTC, the Confirmed DTC, and the freeze data can be cleared with the scan tool clear command.