DTC 53 Gas Mass Sensor Circuit Range Performance. GMC Truck GMC C Pickup

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC C Pickup - 2WD (CNG) 🢒 Engine 🢒 Engine Controls - 5.0L and 5.7L 🢒 DTC 53 Gas Mass Sensor Circuit Range Performance

Handling Electrostatic Discharge Sensitive Parts Notice
Engine Controls Components
CNG Fuel Controls
OBDII Symbol Description Notice

Circuit Description

The Gas Mass Sensor (GMS) provides a frequency signal proportional to the mass-flow of gaseous fuel entering the engine. The GMS actual gas signal varies from about 700 Hz at idle to about 2700 Hz at Wide Open Throttle (WOT).

The GMS desired gas signal from the ECU is an input to the GMS which is a frequency ranging from about 700 Hz to 5000 Hz. This signal, when present, activates the GMS and commands a desired Mixture Control Valve (MCV) position.

The GMS actual gas signal is one of the most important inputs used by the ECU for fuel control while operating on CNG. The GMS provides fuel mass-flow feedback to the ECU which is used to precisely trim the position of the MCV for the required fuel flow rate.

This is a type A DTC.

Conditions for Setting the DTC

The following conditions will set the DTC:

•	The vehicle is in the CNG operation mode.

•	The ECT is between 80°C (176°F) and 105°C (221°F).

•	The CNG fuel sending unit voltage is greater than 1.95 volts (fuel level above 1/8 tank).

•	The battery voltage is greater than 10 volts.

•	The engine speed is higher than 500 RPM.

•	None of the following DTCs are active: 14, 15, 16, 35, 36, 37, 42, 43, 44, 45, 51, 52, 62, 63, 64, 65.

•	There is an out of range signal.

Action Taken When the DTC Sets

The ECU will set DTC 53 and illuminate the MIL lamp after one fault has occurred if a low frequency failure is detected. The ECU will simultaneously initiate a fuel mode switch-over to gasoline. The vehicle will not attempt to operate on CNG again until the next key cycle.

Conditions for Clearing the MIL/DTC

The ECU turns the MIL OFF after 3 consecutive driving trips without a fault condition present. A DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 40°C (72°F) from the start-up coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during that same ignition cycle) or the code clearing procedure has been used.

Diagnostic Aids

Always diagnose ANY VCM codes that are present before beginning this diagnostic procedure.

Diagnose and correct any ECU DTCs that are present pertaining to the O2 sensors, the MAF sensor and GMS DTC 51 and DTC 52 before attempting to diagnose DTC 53.

Any condition that results in incorrect fueling can cause DTC 53 to set. Check for the following conditions:

•	Improper wire harness routing near secondary ignition components and other high voltage sources.

•	MAF sensor DTCs and wiring problems.

•	O2 sensor DTCs and wiring problems.

•	Malfunctioning EVAP system.

•	Incorrect CNG fuel system pressure.

•	Inspect the harness for the following conditions:

-	Backed out terminals

-	Improper mating

-	Broken locks

-	Improperly formed or damaged terminals

-	Poor terminal to wire connection

-	A damaged harness

Important: The GMS actual gas flow and desired gas flow frequencies cannot be monitored in the gasoline mode at any time. These frequencies cannot be monitored in the CNG mode with the Key On/Engine Off. The signals will only be present while operating on CNG and only with the engine in the crank or run modes.

Since DTC 53 causes a switch-over to gasoline when it sets, the conditions that cause it may be monitored before the switch-over by using a Tech 2 scan tool to monitor MAF and a DVOM to monitor GMS actual gas circuit frequency. Compare the readings according to the diagnostic high/low limits in the following table:

MAF g/sec	GMS Ideal Hz*	High Limit Hz	Low Limit Hz
10	955	1067	795
20	1172	1317	985
30	1325	1473	1112
40	1438	1600	1212
50	1526	1724	1290
75	1733	1965	1455
100	1919	2188	1582
150	2207	2463	1792
200	2415	2754	1984
*Actual gas circuit frequency output.

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

This step visually and physically inspects the items that can cause a lean condition in order to determine the cause of the mis-fueling.

This step inspects for HO2 sensor faults by operating the vehicle on gasoline and interrogating the VCM for DTCs.

This step inspects for a fault in the EVAP system which can cause DTC 53 to set.

This step inspects for HO2 sensor wiring problems.

This step inspects for correct fuel system pressures.

This step inspects the GMS ground connection.

This step inspects for improper routing of the wire harness.

Step

Action

Value(s)

Yes

Was the Alternative Fuels (AF) Powertrain On-Board Diagnostic (OBD) System Check performed?

Go to Step 2

Go to Alternative Fuels (AF) Powertrain On Board (OBD) System Check

Visually and physically verify the following items:

•	The HO2 sensor. It must be installed securely. The pigtail harness must not contact the exhaust manifold or the ignition wires.

•	The gasoline fuel pressure regulator for leakage. Refer to Fuel System Diagnosis in Engine Controls - 5.0, 5.7L in the C/K Truck Service Manual.

•	The vacuum hoses for splits, kinks and the proper connections.

•	The throttle body, the intake manifold, the induction hoses and the EGR valve for vacuum leaks.

•	The crankcase ventilation valve, the spring and the O-ring for proper installation.

•	The ECU and the sensor grounds. They should be clean, tight and in the proper location.

•	The VCM and the sensor grounds. They should be clean, tight and in the proper location.

•	The exhaust system for loose connections and leaks.

•	The air intake duct for collapsing or restrictions.

•	The air filter for restrictions.

Was a repair made?

Go to Step 13

Go to Step 3

Remove the AF fuse F1 (1997 models) or the 20A CNG fuse from the underhood fuse-relay center (1998 models).
Start the vehicle.
Perform the AF OBD Trip.

The fuel indicator light will remain OFF due to the removal of the CNG system fuse.

Turn OFF the ignition. Wait 5 to 10 seconds.
Restart the vehicle.
Perform the AF OBD Trip again.
Inspect for VCM DTCs using the scan tool.
Replace the CNG system fuse.

Was a problem found?

Go to the applicable VCM DTC table in Engine Controls - 5.0, 5.7L in the C/K Truck Service Manual

Go to Step 4

Perform the AF Fuel System Diagnosis. Refer to Fuel System Diagnosis .

Was a problem found and repaired?

Go to Step 13

Go to Step 5

Perform the EVAP Control System Diagnosis. Refer to EVAP Control System Diagnosis in Engine Controls - 5.0, 5.7L in the C/K Truck Service Manual.

Was a problem found and repaired?

Go to Step 13

Go to Step 6

Disconnect the HO2S (Bank 1, Sensor 1) connector.
Disconnect ECU connector C001.
Check the HO2S (Bank 1, Sensor 1) signal circuit using a DVOM for resistance greater than the specified value.
Check the HO2S (Bank 1, Sensor 1) signal circuit using a DVOM for continuity to ground.

Was a problem found?

0.5 ohms

Go to Step 11

Go to Step 7

Disconnect the HO2S (Bank 2, Sensor 1) connector.
Disconnect ECU connector C001.
Inspect the HO2S (Bank 2, Sensor 1) signal circuit using a DVOM for resistance greater than the specified value.
Inspect the HO2S (Bank 2, Sensor 1) signal circuit using a DVOM for continuity to ground.

Was a problem found?

0.5 ohms

Go to Step 11

Go to Step 8

Turn ON the ignition.
Inspect for system voltage at the GMS connector using a DVOM connected to ground.

Does the DVOM read within the specified range?

11-13 V

Go to Step 9

Go to Step 11

Turn OFF the ignition.
Verify the continuity of the two ground circuits at the GMS connector to the engine ground using a DVOM.

Is there continuity?

Go to Step 10

Go to Step 11

Inspect for proper routing of the wire harness away from any secondary ignition system components, wires and other high voltage components such as relays, motors, etc.
Correct any improper routing.

Was a problem found and corrected?

Go to Step 13

Go to Step 12

Make the necessary wiring repairs. Refer to Repair Procedures in Electrical Diagnosis in the C/K Truck Service Manual.

Is the action complete?

Go to Step 13

Replace the GMS/MCV. Refer to Gas Mass Sensor/Mixture Control Valve and Mounting Bracket Replacement .

Is the action complete?

Go to Step 13

Clear the DTC.
Verify if the MIL lamp still illuminates after two driving cycles.

Did the MIL illuminate and the DTC set?

Go to Step 2

Go to Step 14

Are any DTCs displayed that have not been diagnosed?

Go to the applicable DTC table

System OK