Manifold Absolute Pressure (MAP) Sensor

1996 PCED OBDI

SECTION 18: Diesel Diagnosis — 7.3L DI Engine

D: Manifold Absolute Pressure (MAP) Sensor

D: Introduction

D1 DIAGNOSTIC TROUBLE CODE (DTC) 0236

DTC 0236 indicates a turbo boost sensor A circuit performance.
Possible causes:

Damaged MAP hose
Damaged MAP sensor
Low turbo boost
Damaged PCM
Intake manifold or crossover leaks

Inspect MAP sensor hose for damage, misrouting or restriction.

Is MAP hose OK and free of any restrictions?

Yes	No
GO to D2.	REPLACE MAP hose. CLEAR DTCs and RETEST.

D2 MAP FREQUENCY CHECK

Disconnect MAP sensor connector.
Connect the MAP sensor tester between the vehicle harness and the MAP sensor.
Connect MAP tester to a DVOM. Set DVOM to frequency scale.
Key on/engine off.

Is frequency reading between 90 hz and 115 hz?

Yes	No
GO to D3.	REPLACE MAP sensor. CLEAR DTCs and RETEST.

D3 MAP SENSOR PRESSURE CHECK

MAP tester still connected.
Remove MAP hose from sensor.
Key on/engine off.
Using Rotunda Pressure Adapter Kit 014-00761 or equivalent (gauge bar), apply 10 psi of pressure to the MAP sensor.

Is frequency reading 145 hz ± 10 hz?

Yes	No
GO to D4.	REPLACE MAP sensor. CLEAR DTCs and RETEST.

D4 MAP PERFORMANCE TEST

Reconnect MAP hose to sensor.
Disconnect MAP hose from intake manifold and install a pressure (boost) gauge.
Road test vehicle and accelerate vehicle to achieve full boost.

Is engine boost 12 psi or greater?

Yes	No
REPLACE PCM. CLEAR DTCs and RETEST.	INSPECT intake manifolds, crossover tubes for leaks. CHECK turbo condition. REFER to appropriate engine section in Powertrain, Drivetrain Service Manual.

D5 KOEO DIAGNOSTIC TROUBLE CODE (DTC) 0237 OR 0235

DTC 0237 (1996 model year) indicates turbo boost sensor A circuit low input. DTC 0235 (1995 model year) indicates MAP signal is inactive. If DTC 0237 is set and the vehicle is a 1995 model, go to D27.
Possible causes:

MAP signal circuit open, shorted to ground, shorted to B+, or shorted to VREF
Open or shorted VREF circuit
Open or shorted signal return circuit
Damaged MAP sensor
Damaged PCM

Key off.
Disconnect MAP sensor connector.
Connect the MAP sensor tester between the vehicle harness connector and the MAP sensor.
Insert the MAP tester banana plugs into a DVOM.

Note: Green light on tester indicates VREF is OK (4.5-5.5 volts) and signal return is OK. Red light indicates VREF is either too low or too high. No lights indicate VREF or signal return are open or shorted.

Key on.

Is green light on?

Yes	No
Go to D6.	Red light "less than 4V" on or no lights, GO to D11. Red light "greater than 6V" on, GO to D14.

D6 MAP SIGNAL SHORT TO GROUND CHECK

Disconnect PCM, inspect for damaged or pushed-out pins, corrosion, loose wires, etc. Service as necessary.
Install breakout box, leave PCM disconnected.
Disconnect MAP sensor harness connector.
Measure resistance from Pin 34 to Pins 25, 51, 76, 77, 91, 103.

Is each resistance greater than 10,000 ohms?

Yes	No
GO to D7.	REPAIR short to ground or signal return in MAP signal Circuit 358 (LG/BK). CLEAR DTCs and RETEST.

D7 MAP SIGNAL SHORT TO VOLTAGE CHECK

PCM disconnected.
MAP connector disconnected.
Key on/engine off.
Measure resistance from Pin 34 to Pins 55, 71 and 97 at the breakout box.

Is each resistance greater than 10,000 ohms?

Yes	No
GO to D8.	REPAIR short to power in MAP signal Circuit 358 (LG/BK) and REPLACE MAP sensor. CLEAR DTCs and RETEST.

D8 MAP SIGNAL SHORT TO VREF CHECK

PCM still disconnected.
MAP connector disconnected.
Key off.
Measure resistance from Pin 34 to Pin 90 at the breakout box.

Is resistance greater than 10,000 ohms?

Yes	No
GO to D9.	REPAIR short to VREF in MAP signal Circuit 358 (LG/BK). CLEAR DTCs and RETEST.

D9 MAP SIGNAL CONTINUITY CHECK

PCM disconnected.
MAP connector disconnected.
Measure resistance from Pin 34 at breakout box to Circuit 358 (LG/BK) at the MAP harness connector.

Is resistance less than 5 ohms?

Yes	No
GO to D10.	REPAIR open MAP signal Circuit 358 (LG/BK). CLEAR DTCs and RETEST.

D10 PCM CHECK

Connect PCM to breakout box.
MAP connector disconnected.
Key on.
Measure voltage on MAP signal Circuit 358 (LG/BK) at MAP harness connector.

Is voltage reading 5 volts ± .5v?

Yes	No
REPLACE MAP sensor. CLEAR DTCs and RETEST.	REPLACE PCM. CLEAR DTCs and RETEST.

D11 VREF VOLTAGE CHECK

Disconnect MAP tester connector from MAP sensor, leaving it connected to vehicle harness.
Key on/engine off.

Is green light on tester now on?

Yes	No
REPLACE MAP sensor. CLEAR DTCs and RETEST.	GO to D12.

D12 VREF CONTINUITY CHECK

Key off.
Disconnect PCM, inspect for damaged or pushed-out pins, corrosion, loose wires, etc. Service as necessary.
Install breakout box, leave PCM disconnected.
Disconnect MAP tester from vehicle harness.
Measure resistance from Pin 90 at breakout box to VREF Circuit 351 (BR/W) at MAP connector.

Is resistance less than 5 ohms?

Yes	No
GO to D13.	REPAIR open in VREF Circuit 351 (BR/W) between PCM and MAP sensor.

D13 SIGNAL RETURN CONTINUITY CHECK

PCM disconnected.
Measure resistance from Pin 91 on breakout box to signal return Circuit 359 (GY/R) at MAP harness connector.

Is resistance less than 5 ohms?

Yes	No
REPLACE PCM. CLEAR DTCs and RETEST.	REPAIR open in signal return Circuit 359 (GY/R).

D14 VREF SHORT TO B+ CHECK

Disconnect PCM, inspect for damaged or pushed-out pins, corrosion, loose wires, etc. Service as necessary.
Install breakout box, leave PCM disconnected.
Key on.
Measure voltage from Pin 90 to ground.

Is voltage reading less than .25 V?

Yes	No
REPLACE PCM. CLEAR DTCs and RETEST.	REPAIR short to B+ in VREF circuit. CLEAR DTCs and RETEST.

D15 KOEO DIAGNOSTIC TROUBLE CODE (DTC) 0238

DTC 0238 indicates turbo boost sensor A circuit high input.
Possible causes:

Damaged MAP sensor
Damaged PCM

Disconnect MAP sensor connector.
Connect the MAP sensor tester between the vehicle harness connector and the MAP sensor.
Insert the MAP tester banana plug into a DVOM. Set DVOM to frequency scale.
Key on/engine off.

Is frequency reading above 125 hz?

Yes	No
REPLACE MAP sensor. CLEAR DTCs and RETEST.	REPLACE PCM. CLEAR DTCs and RETEST.

D16 CONTINUOUS DIAGNOSTIC TROUBLE CODE (DTC) 0237 OR 0235

DTC 0237 (1996 model year) indicates turbo boost sensor A circuit low input. DTC 0235 (1995 model year) indicates MAP sensor signal was inactive. The code was set during normal driving conditions.
Possible causes:

MAP signal circuit open, shorted to ground, shorted to VREF
Open in VREF circuit
Open in signal return circuit
Damaged MAP sensor
Damaged PCM

Disconnect MAP sensor harness connector, and inspect pins for damage.
Connect MAP sensor tester between the vehicle harness connector and MAP sensor.
Insert banana plug into DVOM.
Set DVOM to frequency scale.
Key on, engine off.

Is frequency reading 110 hz ± 5 hz?

Note: MAP connector has no letter identification. Refer to diagram at beginning of this Pinpoint Test for proper pin location.

Yes	No
GO to D17.	REPLACE MAP sensor.

D17 MAP SENSOR CHECK

Lightly tap on MAP sensor while monitoring frequency reading on NGS Tester.

Does reading fluctuate?

Yes	No
REPLACE MAP sensor. CLEAR DTCs and RETEST.	GO to D18.

D18 MAP SENSOR PSI CHECK

Apply 10 psi of pressure with vacuum/pressure pump from Rotunda Pressure Adapter Kit 014-00761 or equivalent.
Tap on sensor while monitoring reading on NGS Tester.

Does reading fluctuate?

Yes	No
REPLACE MAP sensor. CLEAR DTCs and RETEST.	GO to D19.

D19 SIGNAL RETURN HARNESS CHECK

MAP harness connector disconnected.
Measure resistance from Pin A on harness connector to ground.
Observe the resistance value while performing the following:

Grasp the vehicle harness close to the sensor connector. Wiggle, shake vehicle harness while working towards the PCM.

Does resistance reading fluctuate?

Yes	No
REPAIR intermittent open in Circuit 359 (GY/R) as required. CLEAR DTCs and RETEST.	GO to D20.

D20 VREF CIRCUIT CHECK

Key on.
Measure voltage from Pin B on harness connector to ground.
Observe VREF voltage (5v ± .5) while performing the following:

Grasp the harness close to the sensor connector. Wiggle, shake vehicle harness while working towards the PCM.

Does voltage value fluctuate?

Yes	No
REPAIR intermittent open in Circuit 351 (BR/W) as required. CLEAR DTCs and RETEST.	GO to D21.

D21 MAP SIGNAL WIRE CONTINUITY CHECK

Disconnect PCM, inspect for damaged, pushed-out pins, corrosion, loose wires, etc. Service as necessary.
Install breakout box, leave PCM disconnected.
MAP connector disconnected.
Measure resistance from Pin 34 to Circuit 358 (LG/BK) at MAP on harness connector.
Observe resistance value while performing the following.

Grasp harness close to the sensor connector. Wiggle, shake vehicle harness while working towards the PCM.

Does resistance stay below 5 ohms?

Yes	No
GO to D22.	REPAIR intermittent open in Circuit 358 (LG/BK). CLEAR DTCs and RETEST.

D22 MAP SIGNAL WIRE SHORT TO GND

Measure resistance from Pin 34 to Pins 25, 51, 76, 77, 103 on breakout box.
Perform harness shake test.

Does resistance value drop below 10,000 ohms?

Yes	No
REPAIR intermittent short to ground in Circuit 358 (LG/BK). CLEAR DTCs and RETEST.	GO to D23.

D23 MAP SIGNAL WIRE SHORT TO PWR

Key on.
Measure voltage from Pin 34 to ground.
Perform harness shake test.

Does voltage reading go above 0v?

Yes	No
REPAIR intermittent short to PWR in circuit 358 (LG/BK). CLEAR DTCs and RETEST.	Intermittent failure. Unable to VERIFY. CLEAR DTCs.

D24 CONTINUOUS DIAGNOSTIC TROUBLE CODE (DTC) 0238

DTC 0238 indicates turbo boost sensor A circuit high input. This code was set under normal driving conditions.
Possible causes:

Damaged MAP sensor
Damaged circuit

Disconnect MAP sensor connector.
Connect MAP sensor tester between the vehicle harness connector and MAP sensor.
Insert banana plug into DVOM.
Set DVOM to frequency scale.
Key on, engine off.
Observe frequency reading while tapping on sensor.

Does frequency reading go above 125 hz?

Yes	No
REPLACE MAP sensor. CLEAR DTCs and RETEST.	GO to D25.

D25 MAP SENSOR CHECK

Apply 10 psi with vacuum/pressure pump from Rotunda Pressure Adapter Kit 014-00761 or equivalent.
Observe frequency reading while tapping on sensor.

Does frequency reading go above 300 hz?

Yes	No
REPLACE MAP sensor. CLEAR DTCs and RETEST.	GO to D26.

D26 MAP HARNESS CHECK

Using a vacuum pump from Rotunda Pressure Adapter Kit 014-00761 or equivalent, apply 10 in. of vacuum.
Observe frequency reading while performing the following:

Grasp the vehicle harness close to the sensor connector. Wiggle and shake the vehicle while working towards the PCM.

Does frequency reading go above 300 hz?

Yes	No
REPAIR intermittent circuit failure. CLEAR DTCs and RETEST.	FAILURE is intermittent. Unable to duplicate at this time. CLEAR DTCs.

D27 KOEO DIAGNOSTIC TROUBLE CODE (DTC) 0237

DTC 0237 (1995 model year) indicates turbo boost sensor A circuit low input.
Possible causes:

Damaged MAP sensor
Damaged PCM

Disconnect MAP sensor connector.
Using Flex probes from NGS Tester kit, jumper VREF and signal return from harness connector to MAP sensor.
Install jumper from Pin C of MAP sensor to SIG INPUT on NGS Tester.
Select digital measurement on NGS Tester menu.
Select frequency meter.
Use 4V DC scale.
Key on, engine off.

Is frequency reading 110 Hz ±15 Hz?

Yes	No
REPLACE PCM. CLEAR DTCs and RETEST.	REPLACE MAP sensor. CLEAR DTCs and RETEST.