Achieva L4-144 2.4L DOHC VIN T SFI (1996)
Powertrain Control Module: Description and Operation
PCM Inputs
PCM CONTROLLED WARNING LAMPS
The oil level switch, the oil pressure switch and the coolant level switch are connected to the Powertrain Control Module (PCM). If a low oil level
condition, a low oil pressure condition, or a low coolant level condition is detected, the PCM will send a signal to the Instrument Panel Cluster
(IPC). The IPC will receive this signal from the PCM and the IPC will then illuminate the warning lamp.
The electronic instrument cluster uses 3 telltale lamps. A Check Oil telltale lamp that indicates a low oil level condition. A Low Oil Pressure
telltale lamp indicates low engine oil pressure. A Low Coolant Level telltale lamp indicates a low coolant level condition. The purpose of these
lamps are to warn the operator of potential engine damaging conditions. If any of the warning lamps are illuminated, then a condition is present
that may cause engine damage.
OIL LEVEL SWITCH
The oil level switch is an assembly containing a reed switch and magnetic float. When the oil level is normal, the float rests near the reed switch,
causing the switch to close. When the oil level is low, the float rests away from the reed switch causing the contacts to open.
The oil level switch is mounted in the engine oil pan. The oil level switch supplies a ground signal to the PCM when the engine oil level is above a
specific level. If the engine oil level falls below this level, the oil level switch opens and the PCM sends a signal through UART serial data to the
IPC to illuminate the Check Oil telltale lamp.
FUEL PUMP AND ENGINE OIL PRESSURE INDICATOR SWITCH
The fuel pump and engine oil pressure indicator switch has two functions. One is to indicate low engine oil pressure and the other is to supply
battery voltage to the fuel pump in the event the fuel pump relay fails.
The oil pressure portion of the switch has normally closed contacts. The contacts on the oil pressure switch will open when oil pressure exceeds 41
kPa (6 psi). The contacts will close on a decreasing pressure of 14 kPa (2 psi). When the contacts are closed, the oil pressure switch sends a
signal to the PCM. The PCM then sends this signal to the IPC and the oil pressure telltale lamp on the IPC will illuminate.
The fuel pump portion of the switch has normally open contacts that close on an increasing oil pressure of 41 kPa (6 psi), and open on a
decreasing pressure of 14 kPa (2 psi). In the event the fuel pump relay fails, the battery voltage is supplied to the fuel pump through the closed
contacts from the switch.
COOLANT LEVEL SWITCH
The coolant level switch is an assembly containing a reed switch and magnetic float. When the coolant level is normal, the float rests away from
the reed switch, causing the switch to open. When the coolant level is low, the float rests near the reed switch and causes the switch to close.
The coolant level switch is mounted in the radiator surge tank. If the coolant level falls below a specific level, the contacts close, and a signal is
sent to the PCM. The PCM will then send this signal to the IPC to illuminate the coolant level telltale lamp.
