1991/05/01 Caterpillar

Inlet Air Temperature Sensor Added And Fuel Pressure Sensor Removed From Engine Control System

Usage:

3176 (7LG) Truck Engines

SUPPLEMENT: 07/00/91

Truck Engine News, May 1991, Page 4, "Inlet Air Temperature Sensor Added And Fuel Pressure Sensor Removed From Engine Control System " on 3176...7LG Truck Engines. The Parts List chart at the end of the article is not complete. The complete Parts List follows.

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An inlet air temperature sensor and diagnostic code 38 " Inlet Air Temperature Sensor Fault" have been introduced on the 1991 3176 Truck Engine. The fuel pressure sensor, diagnostic code 37 "Fuel Pressure Sensor Fault", and diagnostic code 63 "Low Fuel Pressure Warning" have been eliminated. Current 3176 Truck Engine publications do not reference the inlet air temperature sensor system operation, ECAP screen information, diagnostic code explanation, troubleshooting procedure, and additional parts. This article is intended to be a source of this information, until the publications are updated.

NOTE: This article also includes sections entitled "ECAP Information, " "Diagnostic Information," "Troubleshooting, " and "Parts List." These sections are intended to supplement the present 3176 Truck Engine publications until updated versions are available.

An inlet air temperature sensor has been added to the 1991 3176 Truck Engine to control fuel injection timing during cold inlet air/warm inlet air operation. Diagnostic code 38 "Inlet Air Temperature Sensor Fault" has been added to identify an inlet air temperature sensor system fault. The coolant temperature sensor is also part of the inlet air temperature system strategy. The ECM corrects the inlet air temperature sensor signal for effects of external engine heat based on the engine coolant temperature. The inlet air temperature sensor became effective with engine serial number 7LG02259.

NOTE: The 9X5370 Inlet Air Temperature Sensor is the same sensor that is used for coolant temperature. The sensor is mounted in the top of the inlet manifold, to the rear of the inlet port. The fuel pressure sensor wiring harness connector (J16) is connected to a 4P9612 extension wiring harness that connects to the inlet air temperature sensor (J21). The fuel pressure sensor has been removed from the 3176 Truck Engine. A new personality module has been released for each 3176 Engine Family to control the system strategy.

ECAP (Electronic Control Analyzer Programmer) Information

1. The ECAP will be unable to monitor the Inlet Air Temperature Sensor temperature through the ECM until the June 1991 update SPM (Service Program Module), NEXG4522. (The Coolant Temperature Sensor reading can currently be viewed from an ECAP through the ECM, and is used as part of the Coolant Temperature Sensor Test in the 1991 3176 Engine Troubleshooting Guide, SENR5112.)

2. The Fuel Pressure Sensor reading on the ECAP status screen will be set to 0 psi. Diagnostic Code 37 "Fuel Pressure Sensor Fault" and Diagnostic Code 63 " Low Fuel Pressure Warning" are disabled.

3. Diagnostic code 38 is now enabled. Until the June 1991 ECAP SPM is available, the ECAP will indicate Diagnostic Code 38 as "unassigned". The ECAP user will also see the following message on the ECAP with the NEXG4507 VERSION 1.2 SPM until the new SPM is available:

Show/hide table

NOTICE

This 3176 Truck Functions SPM Version is older than the personality module software version. The integrity of changed parameters and displayed data is not guaranteed. Please order NEXG4507 3176 Truck Functions SPM update. 1 - Read/Change Parameters 2 - Display Status 3 - Display Diagnostic Messages 4 - Monitor/Calibrate Sensors 5 - Interactive Diagnostics

The integrity of the changed parameters and displayed data is not affected by this Personality Module Software update.

The Personality Part Numbers associated with this update are:

250 hp-3E6372

275 hp-3E6373

300 hp-3E6374

325 hp-3E6375

Diagnostic Information for Diagnostic Code 38 " Inlet Air Temperature Sensor Fault"

Conditions Which Generate This Code:

The Electronic Control Module (ECM) detects signal voltage from an Inlet Air Temperature Sensor that is below 0.3 volts DC or above 4.7 volts DC for at least 1/4 of a second.

System Response:

1. The inlet air temperature is artificially set to 90 °C (194°F) by the ECM.

2. The code is current (Diagnostic Lamp, ECAP, or DDT) and is LOGGED in memory.

Troubleshooting:

Inlet Air Temperature Sensor Test

The Inlet Air Temperature Sensor measures the temperature of the inlet manifold air. The sensor is identical to the Coolant Temperature Sensor.

The 3176 Electronic Control Module (ECM) monitors the Inlet Air Temperature Sensor and Coolant Temperature Sensor signals to adjust injection timing. The Inlet Air Temperature Sensor does not affect Cold Mode low idle engine rpm like the Coolant Temperature Sensor.

The sensor operates on 5.0 volts DC, supplied through Pin 10 of the ECM Connector (J4/P4). Note that this voltage supply is common to the Coolant Temperature Sensor also. The return (ground) line for both sensors goes through Pin 35 of the ECM Connector (J4/P4).

Due to the addition of the Extension Wiring Harness, the connector at the Inlet Air Temperature sensor is identified as J21/P21.

NOTE: See chart on Page 5-22 of 3176 Troubleshooting Manual SENR5112 for Service Tools necessary.

1. Inspect connectors, wiring and sensor.

Check ECM Connector (J4/P4), Engine Harness to Extension Harness Connector (J16/P16), and Inlet Air Temperature Sensor Connector (J21/P21), being sure to:

Check connector lock rings.

Perform 10 pound pull test on each pin or wire.

Inspect wiring for damage or abrasion.

Inspect connectors for damage or corrosion. (Refer to P-201: "Inspecting Electrical Connectors" of the 3176 Diesel Truck Engine Troubleshooting Manual, SENR5112 for details.)

Repair any damage, then continue with the next step.

NOTE: The wiring between the Inlet Air Temperature Sensor Connector and the Engine Harness is an extension from what formerly was the Fuel Pressure Sensor Connector. This extension has a plug on the Engine Harness side (P16) AND the Inlet Air Temperature Sensor Connector side (P21).

2. Check Voltage Supply To Sensor.

a. With key OFF, install the Three-Pin Breakout "T" on the extension harness side of the Inlet Air Temperature Sensor Connector (P21) only. Do not connect to J21 (sensor side) at this time.

b. Turn key ON (engine OFF).

c. Measure sensor supply voltage between Pin A of the Connector P21 and Pin B of Connector P21, on the Breakout "T".

Supply voltage should be 5.0 ± 0.5 volts DC.

If OK, supply voltage is normal. Leave Three-Pin Breakout " T" connected and proceed to Step 6 to check open circuit signal line voltage from the ECM.

If NOT OK, the sensor is not receiving correct supply voltage. Reconnect the Inlet Air Temperature Sensor to the extension harness and continue to next step.

3. Check Voltage Supply To Extension Harness.

a. With key OFF, install the Three-Pin Breakout "T" on the engine harness side (J16) of the engine harness to extension harness connector. Do not connect to P16 (extension harness side) at this time.

b. Turn key ON (engine OFF).

c. Measure sensor supply voltage between Pin A of Connector J16 and Pin B of Connector J16, on the Breakout "T".

Supply voltage should be 5.0 ± 0.5 volts DC.

If OK, supply voltage is normal. Repair the fault (short or break) in the extension wiring harness as necessary. Stop.

If NOT OK, the extension harness is not receiving correct supply voltage. Leave the extension harness to the engine harness connector (J16/P16) disconnected and continue to next step.

4. Check Supply Voltage At ECM.

a. With the key OFF, install the 40-Pin Breakout "T" on the ECM Connector (J4/P4).

b. Turn key ON (engine OFF) and measure sensor supply voltage between Connector P4 Pin 10 (+5V) and Connector P4 Pin 35 (Sensor Return Analog) on the "T".

Supply voltage should be 5.0 ± 0.5 volts DC.

If OK, supply voltage is present at the ECM but not at the extension harness. Repair fault in engine harness between the ECM and the extension harness. Stop.

If NOT OK, the ECM is not supplying correct voltage or there is a short to ground in the engine harness between the ECM and the extension harness. Verify that the ECM is receiving correct voltage from the battery. If it is, continue with the next step.

5. Check For Shorts in Engine Wiring Harness.

a. With the key OFF, disconnect the 40-Pin Breakout "T" from ECM Connector (J4).

b. Install the Three-Pin Breakout "T on the engine harness to extension harness connector (J16 - engine harness side) ONLY. Do not connect to P16 at this time.

c. Set the multimeter on the 20,000 Ohm (20K) scale and measure the resistance between Pin A of Connector J16 and Pin B of Connector J16, on the Three-Pin Breakout "T".

Resistance should be more than 20,000 OHMS.

If OK, the voltage supply wire is not shorted to the return wire. If Step 4 found the supply voltage incorrect at the ECM, then the ECM is faulty. Replace the ECM. Stop.

If NOT OK, the voltage supply to the Inlet Air Temperature Sensor is being shorted to ground. The supply and return wires for the Inlet Air Temperature Sensor are common with the Coolant Temperature Sensor. Check that the supply wire for the Inlet Air Temperature Sensor, is not being shorted out by the Coolant Temperature Sensor. Disconnecting J10/P10 will isolate the Coolant Temperature Sensor. If a short is still present, check connectors and harness between the ECM and both the Inlet Temperature Extension Harness and the Coolant Temperature Sensor. Stop.

6. Check Open Circuit Signal Line Voltage From Extension Harness.

NOTE: The ECM supplies a + 5 volts DC open circuit signal line voltage to the Inlet Air Temperature signal wire when the Inlet Air Temperature Sensor is disconnected. This voltage will be used to diagnose wiring harness and/or ECM faults.

a. With key OFF, install the Three-Pin Breakout "T" on the extension harness side of the Inlet Air Temperature Sensor Connector (P21) only. Do not connect to J21 (sensor side) at this time.

b. Turn key ON (engine OFF).

c. Measure the open circuit signal line voltage between Pin C of the Connector P21 and Pin B of Connector P21, on the Breakout "T".

Open circuit signal line voltage should be 5.0 ± 0.5 volts DC.

If OK, open circuit signal line voltage is normal. Proceed to Step 10 to check signal voltage from the sensor.

If NOT OK, the sensor is not receiving correct open circuit signal line voltage. Reconnect the Inlet Air Temperature Sensor to the extension harness and continue to next step.

7. Check Open Circuit Signal Line Voltage From Engine Harness.

a. With key OFF, install the Three-Pin Breakout "T" on the engine harness side (J16) of the engine harness to extension harness connector. Do not connect to P16 (extension harness side) at this time.

b. Turn key ON (engine OFF).

c. Measure the open circuit signal line voltage between Pin C of the Connector J16 and Pin B of Connector J16, on the Breakout "T".

Open circuit signal line voltage should be 5.0 ± 0.5 volts DC.

If OK, open circuit signal line voltage is normal. Repair the fault (short or break) in the extension wiring harness as necessary. Stop.

If NOT OK, the extension harness is not receiving correct open circuit signal line voltage. Leave the extension harness to engine harness connector (J16/P16) disconnected and continue to next step.

8. Check Open Circuit Signal Line Voltage From ECM.

a. With the key OFF, install on 40-Pin Breakout "T" on the ECM Connector (J4/P4).

b. Turn key ON (engine OFF) and measure the open circuit signal line voltage between Connector P4 Pin 39 (Signal Line) and Connector P4 Pin 35 (Sensor Return Analog) on the Breakout "T".

Open circuit signal line voltage should be 5.0 ± 0.5 volts DC.

If OK, open circuit signal line voltage is present at the ECM but not at the extension harness. Repair fault in engine harness between the ECM and the extension harness. STOP.

If NOT OK, the ECM is not supplying correct open circuit signal line voltage or there is a short to ground in the engine harness between the ECM and the extension harness. Verify that the ECM is receiving correct voltage from the battery. It if is, continue with next step.

9. Check For Shorts In Engine Wiring Harness.

a. With the key OFF, disconnect the 40-Pin Breakout "T" from the ECM Connector (J4).

b. Install the Three-Pin Breakout "T" on the engine harness to extension harness connector (J16- engine harness side) ONLY. Do not connect to P16 at this time.

c. Set the multimeter on the 20,000 Ohm (20K) scale and measure the resistance between Pin C of Connector J16 and Pin B of Connector J16, on the Three-Pin Breakout "T".

Resistance should be more than 20,000 ohms.

If OK, the open circuit signal line wire is not shorted to the return wire. If Step 8 found the open circuit signal line voltage incorrect at the ECM, then the ECM is faulty. Replace the ECM. Stop.

If NOT OK, the open circuit signal line wire to the Inlet Air Temperature Sensor is being shorted to ground. Repair engine harness as necessary. Stop.

10. Check Signal Voltage From Sensor

a. Disconnect the Inlet Air Temperature Sensor from the extension harness (P21/J21).

b. Remove the Inlet Air Temperature Sensor from the Inlet Manifold.

c. Connect a Three-Pin Breakout "T" to the Inlet Air Temperature Sensor (J21) and to the extension harness (P21).

d. Immerse the Inlet Air Temperature Sensor into a container of cold water (preferably ice water) along with the thermocouple from the 6V9130 Temperature Adapter Group.

e. Turn the key ON (engine OFF) and measure the sensor signal voltage between Pin C (Inlet Air Temperature Signal) and Pin B (Sensor Return) of the Three-Pin Breakout "T".

f. Use the conversion table (Table A, Page 5-24 of the 3176 Troubleshooting Guide, SENR5112) to determine the water temperature from the sensor voltage readings. Compare temperature found in this table with temperature shown on the Temperature Adapter Group.

The temperature from the table should be within 10°C 18 °F) of the temperature reading from the temperature adapter group.

If OK, voltage is correct for observed temperature. There is not a current problem with the Inlet Air Temperature Senor Circuit. Stop.

If NOT OK, voltage is incorrect for observed temperature or signal is not present. Replace Inlet Air Temperature Sensor. Stop.