Driver′s intension to accelerate is transmitted to ECM through Accelerator Pedal Sensor(APS) . And APS, whose mechanism is same as TPS, is required for ECM to determine optimum fuel injection quantity.
As fidelity of APS is strongly required, APS is devided into two. One is APS1, which outputs main signals and the other is APS2, which monitors APS1 performance.
APS1 and 2 do not share power supply and ground. Normally, APS2 output voltage is the half of APS1 and if the ratio of two signal is out of specified value, error is recognized then, Limp Home mode is activated.
When Limp Home mode is activated, engine speed is fixed at 1200RPM and driving performance is limited to prevent excessive power generation due to APS false signal.
P2123 is set when output voltage of APS 1 is above the maximum value of 4.789V for more than 0.18 sec. This code is due to the short to battery in APS 1 power circuit and signal circuit or open in sensor ground circuit.
Item | Detecting Condition | Possible Cause | ||
DTC Strategy | ● Voltage Monitoring | ● APS 1 Circuit ● APS component | ||
Enable Conditions | ● IG KEY "ON" | |||
Threshold Value | ● When output signal is above the maximum value (above 4789mV ) | |||
Diagnostic Time | ● 180ms | |||
Fail Safe | Fuel Cut | NO | ● APS standard value is 0%. ● Limp home idle is fixed at (1200RPM) | |
EGR Off | NO | |||
Fuel Limit | YES | |||
MIL | YES | |||
Pedal released | Pedal depressed | Sensor Type | |
APS 1 | 0.7V~0.8V | 3.8V~4.4V | Variable resistance type (Potentiometer) |
APS 2 | 0.275V~0.475V | 1.75V~2.35V |
Fig.1) APS 1 and APS 2 signals are measured simultaneously, Check if output value is rising and APS 2 is 1/2 of APS 1 signal.
APS 2 Ground checking signal is for ECM to monitor APS 2. This signal drops APS 2 output voltage to below 200.39mV per 200msec. If APS 2 output voltage does not drop to below 200.39mV, ECM sets DTC as recognizing ground circuit error of APS 2 .
※ The waveform below 200.39mV is not detectable in Ground checking signal waveform of APS 2 signal. Instead, the waveform which drops a little is detected. If APS 2 data of "SERVICE DATA" on the Scantool varies from 350mV to 0mV periodically, it means it works well.
Connect GDS to Data Link Connector (DLC).
Warm engine up to normal operating temperature.
Turn "OFF" electrical devices and A/C.
Monitor "ACCEL PEDAL SENSOR", "ACCEL PEDAL SENSOR 1", "ACCEL PEDAL SENSOR 2 " parameter on the GDS.
Specification : at idle( 0% ) ACCEL PEDAL SENSOR 1 : 600mV~800mV
Fig.1) APS output data at warm idle. Check if output value is rising and "ACCEL PEDAL SENSOR 2" is 1/2 of "ACCEL PEDAL SENSOR 1" signal.
Fig.2) APS output data at wide open throttle status.
Electrical systems consist of a lot of harness and connectors, poor connection of terminals can cause various problems and damge of component.
Perform checking procedure as follows.
Check damage of harness and terminals : Check terminals for contact resistance, corrosion and deformation.
Check connecting condition of ECM and component connector : Check terminal seperation, damage of locking device and connecting condition between terminal and wiring.
Disconnect the pin which requires checking at male connector and insert it to the terminal at female connector for checking connecting condition. ( after checking, reconnect the pin at correct position. )
Is the problem found?
 | ▶ Repair the trouble causing part and go to "Verification of Vehicle Repair". |
 | ▶ Go to "Power Circuit Inspection". |
IG KEY "OFF", ENGINE "OFF".
Disconnect APS connector.
IG KEY "ON".
Measure the voltage between power terminal of APS harness connector and chassis ground.
Specification : 4.8V~5.1V
Is the measured voltage within the specification?
| ▶ Go to "Signal Circuit Inspection". |
| ▶ If the measured voltage is not within the specified value, find and repair short to battery in APS 1 power circuit and go to "Verification of Vehicle Repair". |
Check open in signal circuit
IG KEY "OFF", ENGINE "OFF".
Disconnect APS connector and ECM connector.
Check continuity between signal terminal of APS harness connector and signal terminal of ECM harness connector.
Specification : Continuity (below 1.0Ω)
Is the measured resistance within the specification?
| ▶ Go to "Check short to battery in signal circuit" as follows. |
| ▶ Repair open in signal circuit and go to "Verification of Vehicle Repair". |
Check short to battery in signal circuit
IG KEY "OFF", ENGINE "OFF".
Disconnect APS connector and ECM connector.
IG KEY "ON".
Measure the continuity between signal terminal of APS harness connector and chassis ground.
Specification : 0.0V~0.1V
Is abnormal voltage detected in signal circuit with both connector disconnected?
| ▶ Repair short to battery and go to "Verification of Vehicle Repair". |
| ▶ Go to "Ground Circuit Inspection". |
IG KEY "OFF", ENGINE "OFF".
Disconnect APS connector.
IG KEY "ON".
Measure the voltage between power terminal of APS connector and chassis ground. [ TEST "A" ]
Measure the voltage between power terminal of APS harness connector and ground terminal of APS harness connector. [ TEST "B" ]
( Power terminal : Check + prove , Ground Terminal : Check - prove )
Specification : [TEST "A"] Voltage - [TEST "B"] Voltage = below 200mV
Is the measured voltage within the specification?
| ▶ Go to "Component Inspection". |
| ▶ When "B" voltage is not detected : Repair open in ground circuit and go to "Verification of Vehicle Repair". ▶ When the voltage difference between "A" and "B" is above 200mV : Eliminate the causes of excessive resistance and go to "Verification of Vehicle Repair". |
IG KEY "OFF", ENGINE "OFF".
Disconnect APS connector .
Check resistance for each terminal refering to Resistance characteristic table.
Specification : Resistance characteristic table for each terminal
checking point | Resistance( KΩ 20℃ ) | Characteristic | Component Connector Shape | ||
Pedal Depressed | Pedal Released | ||||
APS 1 | 5(power)-4(ground) | 1.0±0.1KΩ | 1.0±0.1KΩ | Unchanged |  |
5(power)-3(signal) | 1.8±0.1KΩ | 1.1±0.1KΩ | Resistance drops | ||
3(signal)-4(ground) | 1.1±0.1KΩ | 1.8±0.1KΩ | Resistance rises | ||
APS 2 | 6(power)-2(ground) | 2.0±0.1KΩ | 2.0±0.1KΩ | Unchanged | |
6(power)-1(signal) | 2.9±0.1KΩ | 2.1±0.1KΩ | resistance drops | ||
1(signal)-2(ground) | 1.1±0.1KΩ | 1.8±0.1KΩ | resistance rises | ||
Are resistances for each terminal measured correctly?
| ▶ Go to "Verification of Vehicle Rapair". |
| ▶ Replace APS and go to "Verification of Vehicle Rapair". |
After a repair, it is essential to verify that the fault is corrected.
After connecting GDS select "Diagnostic Trouble Codes(DTCs)" mode to and then clear DTC.
Drive the vehicle within DTC Enable conditions in General information.
After selecting "Diagnostic Trouble Codes(DTCs)" mode and check DTC is recorded again.
Are any DTCs recorded ?
| ▶ Go to the DTC guide of recorded NO. in GDS. |
| ▶ System operates within specification. |
