Diagnostic Aids

Perform this test when directed by QUICK TEST or CIRCUIT TEST S. Barometric pressure sensor output is digital and must be measured using an oscilloscope or MAP/BARO tester. To prevent replacement of good components, be aware the following non-EEC related areas may be cause of problem:

• Unusually high or low atmospheric barometric pressure.
• Kinked or blocked vacuum lines.
• Engine mechanical condition (compression, timing, etc.).

This test is intended to diagnose the following:

• MAP/BARO sensor.
• Wiring harness circuits (VREF, MAP/BARO SIG and SIG RTN).
• MAP vacuum line.
• Powertrain Control Module (PCM).

Application	Wire Color
All Models	Brown/White

Application	Wire Color
"E" Series (AODE) (1)	Dark Blue/Light Green
Except "E" Series (AODE)	Light Green/Black
(1) AODE transmission is identified by letter "U" on Vehicle Safety Compliance Label attached to left door pillar.

Application	Wire Color
All Models	Gray/Red

Manifold Vacuum: In. Hg	Frequency: Hz
0	159
3	150
6	141
9	133
12	125
15	117
18	109
21	102
24	95
27	88
30	80

Barometric Pressure: In. Hg	Frequency: Hz
17.1	122.4
18.3	125.5
19.5	128.7
20.7	131.9
21.8	135.1
23.0	138.3
24.2	141.8
25.4	145.4
26.6	148.9
27.7	152.5
28.9	156.1
30.1	159.6
31.0	162.4

1) Code 22/126: Check Power To MAP/BARO Sensor  Code 22/126 indicates MAP/BARO sensor is out of self-test voltage range (1.4-1.6 volts). Following are possible causes of this code:

• Vacuum trapped at MAP/BARO sensor.
• High atmospheric pressure.
• MAP/BARO signal circuit open between sensor and PCM.
• MAP/BARO signal circuit shorted to VREF, SIG RTN or GND.
• VREF circuit open at sensor.
• SIG RTN circuit open at sensor.
• Faulty MAP/BARO sensor.
• Faulty PCM.

Turn ignition off. Disconnect MAP/BARO sensor from wiring harness. Connect MAP/BARO tester between wiring harness and MAP/BARO sensor. Connect banana plugs of tester into DVOM. Set DVOM on 20-volt scale. Turn ignition on. If Red light or no light is on, VREF is out of range. Go to step 2). If Green light is on, VREF is okay. Go to step 3).

2) Check Power At Sensor Wiring Harness Connector  Disconnect MAP/BARO sensor. Turn ignition on. If Green light on tester is lit, replace MAP/BARO sensor and repeat QUICK TEST. If Green light is not on, remove MAP/BARO tester. Connect MAP/BARO sensor, and go to CIRCUIT TEST C.

3) Check MAP/BARO Sensor Output  With MAP/BARO tester connected and ignition on, measure sensor output voltage. See MAP SENSOR VOLTAGE OUTPUT table. If output voltage is within range for altitude in which vehicle is being tested, remove MAP/BARO tester and go to step 4). If output reading is not within range, remove MAP/BARO tester and go to step 5).

If possible, measure output voltage of several known good MAP/BARO sensors on available vehicles. Average voltage reading will be typical for location and time of testing.

Elevation (Feet)	Volts
0	1.59
1000	1.56
2000	1.53
3000	1.50
4000	1.47
5000	1.44
6000	1.41
7000	1.39

4) Check MAP/BARO SIG Circuit Continuity  Turn ignition off. Disconnect MAP/BARO sensor wiring harness connector. Disconnect PCM 60-pin connector. Inspect it for damaged wiring, and repair as necessary. Install Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between MAP/BARO SIG terminal at sensor wiring harness connector and test pin No. 45. If reading is less than 5 ohms, replace PCM and repeat QUICK TEST. If reading is 5 ohms or more, repair open MAP/BARO SIG circuit and repeat QUICK TEST.

5) Check MAP/BARO SIG Circuit For Short To VREF, SIG RTN & Ground  Turn ignition off, and wait 10 seconds. Disconnect PCM 60-pin connector. Inspect it for damaged wiring, and repair as necessary. Install Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Disconnect wiring harness at MAP/BARO sensor. Measure resistance between test pin No. 45 and test pins No. 26, 40, 46 and 60. If any resistance is less than 10,000 ohms, repair short circuit. Repeat QUICK TEST. If all readings are 10,000 ohms or more, replace MAP/BARO sensor. Repeat QUICK TEST.

7) KOER Code 22/126: Check For EGR-Related Codes  Code 22/126 indicates MAP/BARO signal is out of self-test range during KOER SELF-TEST. Possible causes for this code are:

• Excess EGR flow.
• Damaged or mis-routed MAP/BARO sensor vacuum hose.
• Faulty MAP/BARO sensor.

If Code 31/327, 32/328, 33/332, 34/334, 35/337, 326 or 336 is present, perform applicable CIRCUIT TEST. See SERVICE CODE REFERENCE CHARTS. If codes are not present, go to step 8).

8) Check MAP Sensor Operation  Turn ignition off. Disconnect vacuum hose from MAP sensor. Connect vacuum pump to MAP sensor, and apply 18 in. Hg. If vacuum is not held, replace sensor and repeat QUICK TEST. If MAP sensor holds vacuum, release vacuum and go to step 9).

9) Attempt To Eliminate Code 22/126  Plug MAP sensor vacuum supply hose. Start engine, and run it at 1400-1600 RPM. Slowly apply 15 in. Hg to MAP sensor. Perform KOER SELF-TEST. Check for Code 22/126, disregarding any other codes at this time. If Code 22/126 is still present, replace MAP sensor. If Code 22/126 is not present, inspect MAP sensor vacuum supply hose. If hose is okay, service other codes at this time. If no other code is present, check engine mechanical condition for cause of low vacuum.

10) Code 72/129: Repeat Dynamic Response Test  Code 72/129 indicates MAP sensor output did not change enough during dynamic response test. Possible causes for this code are:

• System failed to detect Wide Open Throttle (WOT).
• Damaged or mis-routed MAP/BARO sensor vacuum hose.
• Faulty MAP sensor.

Repeat KOER SELF-TEST. Ensure complete WOT is performed during dynamic response portion of test. If KOER Code 72/129 is still present, go to step 11). If code is not present, service any other codes as necessary.

11) Continuous Memory Code 81/128  Continuous Memory Code 81/128 indicates MAP sensor vacuum has not changed more than 2 in. Hg during normal vehicle operation. Possible causes for this code are:

• MAP sensor vacuum hose is improperly routed, blocked or is leaking.
• MAP sensor is leaking.

Check vacuum lines for correct routing. Refer to Vehicle Emission Control Identification (VECI) decal. Check for loose connections, kinks and blockage. Repair vacuum lines as necessary. If vacuum lines are okay, go to step 12).

12) Check MAP Sensor Operation  Turn ignition off. Disconnect vacuum supply hose from MAP sensor. Attach vacuum pump to MAP sensor. Apply 18 in. Hg to MAP sensor. If MAP sensor holds vacuum, release vacuum and go to step 13). If sensor does not hold vacuum, replace MAP sensor and repeat QUICK TEST.

13) Verify Vacuum To MAP Sensor Decreases During Dynamic Response Test  Turn ignition off. Use a "T" fitting to install a vacuum gauge in MAP sensor vacuum hose. Perform KOER SELF-TEST while observing vacuum gauge. If vacuum decreases by more than 10 in. Hg during dynamic response test, replace MAP sensor and repeat QUICK TEST. If vacuum does not decrease by more than 10 in. Hg, EEC-IV system is okay. Check for engine mechanical problems affecting engine vacuum.

90) Continuous Memory Code 22/126  Code 22/126 indicates MAP/BARO sensor was out of self-test range (1.4-1.6 volts) during normal driving conditions. Possible causes for this code are:

• Faulty MAP/BARO sensor.
• Faulty wiring harness or connectors.
• Unusually high or low barometric pressure.

Enter CONTINUOUS MONITOR MODE (WIGGLE TEST). Observe test equipment while performing following:

• Connect a vacuum pump to MAP/BARO sensor.
• Slowly apply 25 in. Hg to sensor.
• Slowly bleed off vacuum from sensor.
• Lightly tap on sensor (to simulate road shock).
• Wiggle sensor connector.

If a fault is indicated, disconnect sensor and inspect connectors. Repair if necessary. If connectors are okay, replace MAP/BARO sensor. Repeat QUICK TEST. If a fault is not indicated, go to step 91).

91) Check EEC-IV Wiring Harness  Stay in wiggle test. Observe analog VOM or scan tester for indication of fault while bending or wiggling small sections of harness from sensor connector to firewall, and from firewall to PCM. If fault is indicated, isolate fault in harness and repair as necessary. Repeat QUICK TEST. If no fault is indicated, go to step 92).

92) Check PCM & Wiring Harness Connectors  Turn ignition off, and wait 10 seconds. Disconnect PCM 60-pin connector. Inspect connectors and terminals for damage. Repair if necessary. If connectors and terminals are okay, fault cannot be duplicated at this time. Testing is complete. Refer to INTERMITTENTS in TESTS W/O CODES article in the ENGINE PERFORMANCE Section.