Exhaust Gas Recirculation: Testing and Inspection

Diagnostic Codes:
P1400/P 0400, P1401, P1408, P1409

Monitoring Procedure
The diagnostics for the EGR valve are split into five parts. Range tests check the EGR thermistor and the pintle position sensor. The controller and pintle position sensor are used to monitor the difference between the target and actual positions of the pintle.

The EGR thermistor is used to verify the flow of exhaust gas in the EGR system. The Pulse Width Modulated (PWM) drive circuit provides open/short circuit detection.

Pintle Control
The difference between the target and actual pintle positions is monitored; if it continually exceeds the limit over a set time period then a fault is registered.

Range Tests
The pintle position sensor input is monitored to detect a high or low out of range value; if it continually exceeds the limit over a set time period then a fault is registered. The EGR thermistor is monitored to detect a high out-of-range temperature.

Flow Rate
When the engine reaches test condition; i.e. engine speed and load are within limits, coolant and air temperatures are above the minimum setting and the throttle position is below the limit; the EGR temperature is monitored and if it does not rise above a limit within the set time period, then a fault event has occurred. When sufficient fault events have occurred then a fault is registered.

PWM Drive Hardware
The ECM, Pulse Width Modulated (PWM) drive hardware will report open or short circuit faults directly. If the Pintle position sensor has an out-of-range fault then the EGR will be disabled. The strategy will report to the Diagnostic Status Manager (DSM) when an EGR fault is present and the DSM will then decide whether to store a fault code and illuminate the MIL Lamp.

Fig. 2 EGR Valve, Section View:

EGR Valve
The EGR valve consists of three main parts; the Solenoid, Pintle and Seat, and the Pintle Position Sensor. The Solenoid provides a unidirectional magnetic field to act upon the armature, which is connected to the Pintle. The resulting force acts to pull the Pintle away from the Seat so allowing exhaust gas to flow into the inlet manifold. Movement of the armature and pintle is resisted by three forces; pressure drop across the pintle and seat area, gravity, and spring load from the pintle position sensor.

The continuously variable control of the flow of exhaust gas into the inlet manifold is achieved by the pintle position sensor providing feedback to the ECM for closed loop control of the pintle position. Pintle position feedback allows the ECM to calculate fuel and spark corrections as well as exhaust gas flow rate. The EGR Function Sensor, situated on the inlet manifold between the throttle body and the EGR valve, is used to verify the flow of exhaust gas in the EGR system.

Fig. 1 EGR & Manifold, Section:

Fig, 2 Interface Between ECM & EGR (low Power):

Fig. 3 Interface Between ECM & EGR ( High Power):

Interface Between ECM And EGR

EGR Sensor - Open Circuit
EGR Flow or Function Sensor Open Circuit, P O4OO

The EGR temperature is monitored when the following conditions are met; engine speed and load are within limits, coolant and air temperatures are above their threshold figures and the throttle position is below it's threshold setting. If the temperature, measured by the EGR thermistor, does not rise above a given setting within a time limit, on a number of occasions, then a fault is registered.

Possible causes of fault:
- EGR function sensor or harness open circuit
- Insufficient gas flowing in EGR circuit due to a leak
- EGR function sensor loose
- EGR function sensor contaminated or blocked
- Insufficient gas flowing due to a blocked pipe or valve
- At TP or MAFS problem affecting test

EGR Valve Position Control
EGR Valve Position Control, P1400

The ECM monitors the difference between actual and demanded pintle valve position. If the pintle position error exceeds 10 % for a set time period, then a pintle valve position fault is registered.

Possible causes of fault:
- EGR pintle position sensor - incorrect voltage, partial short circuit or open circuit on sensor harness
- Obstruction in valve
- Valve seized
- ECM and ignition switch problem
- ECM to EGR drive stage problem
- ECM to EGR control fault

EGR Valve Position Circuit
EGR Valve Position Circuit, P1401

The pintle valve position sensor input is monitored to detect a high or low out-of-range value, continuously for a time period.

Signal range: 0 to 5 volts
Low out-0f-range threshold: 0.37 volts
High out-of-range threshold: 4.80 volts

Possible causes of fault:
- EGR pintle sensor harness open circuit or short circuit to supply or ground
- EGR pintle sensor supply open circuit or short circuit to battery voltage or ground
- EGR pintle sensor ground open circuit or short circuit to supply
- EGR pintle sensor fault
- ECM interface circuit error

Fig. 1 EGR Function Sensor Location:

Fig. 2 EGR Function Sensor Assembly:

EGR Function Sensor
EGR Function Sensor, P1408

EGR temperature is controlled to a maximum of 400 °C. The function sensor output is checked for a high, out-of-range, temperature; when this occurs more than a given number of times then a fault is present.

Possible causes of fault:
- Harness short circuit to ground or supply
- EGR function sensor fault
- ECM interface circuit fault

The EGR function sensor output varies with temperature, as follows:
- 4.397 V at 100 °C.
- 3.696 V at 200 °C.
- 0.54 V at 400 °C.

EGR Valve Circuit
EGR Valve Circuit, P1409

The ECM valve drive hardware will report open or short circuit faults directly.

Possible causes:
- EGR drive harness open circuit or short circuit
- EGR drive solenoid fault open circuit or short circuit
- EGR driver fault

Fig.1 Sensor Resistance With Respect To Temperature:

Figure 1 shows a graph of the EGR function sensor resistance with respect to temperature.

Fig. 2 Test Points For Calculation:

The voltage level for any temperature may be calculated by taking the following readings and substituting them into the formula. Figure 2 shows the test points.

Formula: VT = (RT x 5V) : (1k8 + RT)

Examples:
20 °C RT = 2M5 VT = 4.996 V
50 °C RT = 635K VT = 4.994 V
100 °C RT = 85k3 VT = 4.397 V
200 °C RT = 5k10 VT = 3.696 V
400 °C RT = 0k22 VT = 0.540 V