PEC control module position / design / function

S07.52-3012-06

Task

 Controlling the following systems in line with the analysis of the input signals:
– Fuel injection system
– Ignition system
– Idle speed control
– Emission control system

 Monitoring inputs/outputs, checking plausibility and storing faults

 Forming substitute values for "Emergency running mode" if no signal received

 Automatically recognizing mechanical end stop of the closed throttle valve

 Self-adaptation of mixture formation

 Automatically recognizing vehicle version

1 Connection of crankshaft position sensor

2 Electrical connection at chassis side

3 Connection of intake manifold cable

4 Connection of variable reference resistor

5 Electrical connection at engine side

A13 PEC control module

Function

The PEC control module (A13) is supplied with voltage directly by circuits 15 and 30.

The PEC control module (A13) detects the intake manifold pressure as the principal measured varialble for determining the fuel injection time, by means of an integral pressure sensor. It detects further input signals and actuates outputs in line with the operating conditions.

Inputs:

– Vehicle ground (ground at right of engine compartment)

– Voltage supply circuit 30 (terminal block circuit 30)

– Voltage with ignition on: circuit 15 (terminal block circuit 15)

– Intake manifold pressure (line to intake manifold)

– Coolant temperature signal (coolant temperature sensor)

– Intake air temperature signal (intake air temperature sensor)

– O2 sensor signal (heated O2 sensor)

– Crankshaft position sensor (flywheel segments)

– Throttle valve position (idle speed control actuator)

– Variable reference resistor (adaptation of ignition and injection map)

– Vehicle speed signal (instrument cluster)

– AC compressor on signal (AC control module)

– Ground point in right of engine compartment (recognition of manual transmission)

– Automatic transmission control module (control during gear shifts)

– Starter lockout switch (recognition of automatic transmission and selector lever position P/N)

Outputs:

– Fuel pump relay

– Ignition coil actuation (cylinders 1+4) and (cylinders 2+3)

– Actuation of ignition coils at ground side

– Fuel injectors (cylinders 1+4) and (cylinders 2+3)

– O2 sensor heater

– Idle speed control actuator

– Engine speed signal (datalink connector)

– Engine speed signal (e.g. tachometer, AC control)

– Purge valve (mixture enrichment)

– Exhaust flap switchover valve (rapid catalytic converter heating-up)

– Electronics ground for temperature sensors and idle speed control actuator

– Information on engine torque and throttle valve position to automatic transmission control module

– Fault memory output to datalink connector

Diagnosis/fault storage

All inputs and outputs are checked for plausibility during operation. Faults detected are stored in the fault memory. The PEC control module (A13) makes the following distinctions during fault output:

– Faults which are present as current faults

– Faults which were present over a certain period (longer than 3seconds)

– Sporadic open circuits (e.g. loose contacts) which have occurred more than 5 times during a trip

The faults remain stored when ignition "OFF", but are erased after disconnecting the "vehicle battery" or disconnecting the "control module socket at the vehicle side".

Faults are automatically erased in the fault memory if the same fault no longer occurs within 19 successive identical trips.

A trip for the PEC control module (A13) is completed if:

– Vehicle speed > 10 km/h

– Engine speed > 700 rpm

– Ignition "OFF" > 3 minutes

The faults stored can be read and erased at the datalink connector with ignition "ON" or when "engine running" using the hand-held tester (HHT).

Note on ignition system

When the engine is running, the PEC control module (A13) constantly monitors the primary voltage pattern and primary current pattern of the ignition coils and, on the basis of this monitoring, is able to detect whether faults exist over a total of approx. 50 ignitions.

– Ignition coil (monitoring primary current)

– Secondary ignition circuit (monitoring primary voltage)

If a fault is detected, the corresponding fuel injectors are no longer actuated in groups in order to protect the catalytic converter from excessive thermal stresses. If the fault no longer occurs over a total of approx. 255 ignitions, the fuel injectors are again operated.

Forming substitute values for "emergency running mode" if no signal received

If input signals are not received, the PEC control module (A13) forms a substitute value on the basis of other signals in order to maintain the proper operation of the system.

Example:

If no signal is received from the pressure sensor in the PEC control module (A13), a load signal is formed on the basis of engine speed and throttle valve position, and this is used for determining the injection time.

Automatic recognition of mechanical end stop of closed throttle valve

The PEC control module (A13) has to recognize the mechanical end stop of the closed throttle valve in order to ensure trouble-free operation of the idle speed control.

Recognition is performed with ignition "ON", accelerator pedal "not" operated (selector lever in P/N). The throttle valve is moved to the end stop by the servomotor integrated in the idle speed control (ISC) actuator. The mechanical end stop of the closed throttle valve is detected by the idle speed control (ISC) actuator and stored in the control module.

Automatic recognition of vehicle version

When the vehicle is first operated (vehicle speed > 10 km/h), the PEC control module (A13) recognizes, on the basis of the inputs, the following vehicle versions and stores them in the PEC control module (A13).

– Manual/automatic transmission

– Catalytic converter/no catalytic converter

Note

The "recognition of vehicle version" can be re-activated at the datalink connector using the hand-helt tester (HHT).

When this is done, the following actions are performed:

– Fault memory erased

– Stored values for self-adaptation of mixture formation reset

– Recognition of mechanical stop of closed throttle valve performed

The "recognition of vehicle version" is also activated if the PEC control module (A13) is disconnected and re-connected.

Self-adaptation of mixture formation

If the PEC control module (A13) detects a variation of lambda=1 (corresponds to 14.7 kg air to 1 kg fuel) from the signal supplied by the O2 sensor in the lambda closed-loop control mode, the mixture is continuously corrected by altering the injection time until lambda=1 is restored. The correction in th direction of "rich" or "lean" mixture is in each case max. 25 %. The correction is stored by the PEC control module (A13).

This ensures that the mixture composition in the open-loop mode is neither too "rich" nor to "lean".

Self-adaptation is performed in:

– Idling range

– Part load range

Note

The stored values of self-adaptation can be displayed at the datalink connector using the hand-held tester (HHT).

After completing repair work, such as replacing the PEC control module (A13), or the idle speed control (ISC) actuator, the PEC control module (A13) is once again automatically adapted.