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HOMESERVICE MANUALSCHEVROLET1987STEP VAN P20, 7.4 W, AUTOMATIC, 400/M40REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 12 (ENGINE CONTROLS - TESTS W/CODES - 4.3L)SELF-DIAGNOSTIC SYSTEMREADING TROUBLE CODES
1987 Chevrolet Step Van P20, 7.4 W, Automatic, 400/M40

Reading Trouble Codes

1987 Chevrolet Step Van P20, 7.4 W, Automatic, 400/M40SECTION Reading Trouble Codes
WARNING: This page does not describe the selected car, but rather 13 other vehicles, including the 1994 Oldsmobile Bravada, 1994 GMC Vandura, 1994 GMC Sonoma, 1994 GMC Safari, and 1994 GMC Rally. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: Trouble codes retrieved from ECM/PCM/VCM may be related to either engine or transmission. For engine-related codes, use this article. For transmission-related codes, see appropriate G - ELECTRONIC TRANSMISSION TESTS W/ CODES article in the ENGINE PERFORMANCE section below. To identify whether codes relate to transmission or engine, see TROUBLE CODE IDENTIFICATION table.
  • G - TESTS W/CODES - ELECTRONIC TRANSMISSION (for Astro & Safari)
  • G - TESTS W/CODES - ELECTRONIC TRANSMISSION (for "S" & "T" Series)
  • G - TESTS W/CODES - ELECTRONIC TRANSMISSION (for "C" & "K" Series)
  • AUTO TRANS DIAGNOSIS - 4L60-E & 4L80-E (For "G" & "P" Series)

The ECM stores component failure information under a related trouble code which can be recalled for diagnosis and repair. Read trouble codes by counting Malfunction Indicator Light (MIL) flashes or with diagnostic scan tester connected to the Data Link Connector (DLC). The tester is faster, and capable of reading information which would require testing individual ECM and sensor/solenoid connector terminals with a digital voltmeter. See SCAN TESTER DATA  table and SCAN TESTER USAGE  .

NOTE: When using a scan tester, there is a time delay between serial data updates. For instantaneous response, a digital voltmeter must be used.

If scan tester is not available, MIL flashes can be read by grounding DLC terminal with ignition on and engine off. For example, FLASH, FLASH, pause, FLASH, longer pause, indicates Code 21. The first series of flashes are the first digit of trouble code. The second series of flashes are the second digit of trouble code. Trouble codes are displayed starting with the lowest code. Each code is displayed 3 times and will continue as long as DLC is grounded.

NOTE: Trouble codes will be recorded at various operating times. Some codes require sensor or switch operation for 5 seconds and others may require longer under certain conditions. Some codes may not set in a service bay operational mode.
TROUBLE CODE ID (EXCEPT 4.3L M/T "S" & "T" SERIES PICKUP)

Code Probable Cause
12 No Engine Speed Sensor Reference Pulse
13 Open Oxygen Sensor Circuit
14 CTS Voltage Low (Sensor Or Signal Line Grounded)
15 CTS Voltage High (Sensor Or Signal Line Open)
16 (1) VSS Buffer Fault (4.3L) Trans. Output Speed Signal Low
21 TP Sensor Voltage High (Open Circuit Or Misadjusted TP Sensor)
22 TP Sensor Voltage Low (Circuit Grounded)
23 Intake Air Temperature Low
24 (2) Vehicle Speed Sensor Circuit
25 Intake Air Temperature Sensor Voltage Low
28 (3) Transmission Range Pressure Switch
32 EGR Circuit
33 MAP Voltage High (Circuit Open Or Short To Voltage)
34 MAP Voltage Low (Circuit Open Or Short To Ground)
35 IAC System Fault
36 Idle Speed Control Actuator "C", "K" & "P" Series A/T
37 (3) Brake Switch Stuck Off (4L60E/4L80E)
38 (3) Brake Switch Stuck Off (4L60E/4L80E)
39 (3) TCC Stuck Off
42 EST Circuit Fault
43 Knock Sensor Circuit Fault
44 Lean Exhaust Indicated
45 Rich Exhaust Indicated
51 PROM Error (Faulty/Incorrect PROM)
52 (3) Long System Voltage High (4L60E/4L80E)
52 PROM/CALPAC Error (Faulty/Incorrect PROM/CALPAC)
53 (2) System Voltage High (Charging System Problem)
54 Fuel Pump Circuit Voltage Low
55 ECM/PCM/VCM Error
58 (3) TFT Sensor Circuit Low
59 (3) TFT Sensor Circuit High
66 (3) 3-2 Control Solenoid Fault (4L60E)
67 (3) TCC Solenoid Circuit Fault (4L60E)
68 (3) Overdrive Ratio Error (Engine RPM Greater Than Input Speed)
69 (3) Torque Converter Stuck On (4L60E/4L80E)
72 (3) VSS Signal Loss (4L60E/4L80E)
73 (3) Force Motor (Pressure Control Solenoid) Error
75 (3) System Voltage Low (Charging System Problem)
79 (3) Transmission Fluid Temperature High (4L60E/4L80E)
81 (3) 2-3 Shift Solenoid Circuit Fault (4L60E/4L80E)
82 (3) 1-2 Shift Solenoid Circuit Fault (4L60E/4L80E)
83 (3) QDM TCC Solenoid Circuit Fault (4L80E)
85 (3) Undefined Gear Ratio (4L80E)
86 (3) Low Gear Ratio (4L80E)
87 (3) High Gear Ratio (4L80E)
(1) Models equipped with 4L60E transmission, and 4.3L "S" and "T" Series utility vehicles with manual transmission.
(2) Common gasoline engine and transmission code covered in this article.
(3) Transmission code. For automatic transmission code diagnosis, see appropriate G - ELECTRONIC TRANSMISSION TESTS W/ CODES article in this section. See bullet list below this table.
  • G - TESTS W/CODES - ELECTRONIC TRANSMISSION (for Astro & Safari)
  • G - TESTS W/CODES - ELECTRONIC TRANSMISSION (for "S" & "T" Series)
  • G - TESTS W/CODES - ELECTRONIC TRANSMISSION (for "C" & "K" Series)
  • AUTO TRANS DIAGNOSIS - 4L60-E & 4L80-E (For "G" & "P" Series)
    TROUBLE CODE ID (4.3L "S" & "T" SERIES PICKUP M/T)

    Code Probable Cause
    P0107 MAP Signal Voltage Low (4.3L)
    P0108 MAP Signal Voltage High (4.3L)
    P0122 TP Sensor Circuit Signal Voltage Low
    P0123 TP Sensor Circuit Signal Voltage High
    P0131 HO2S Circuit Low Signal Voltage
    P0132 HO2S Circuit High Signal Voltage
    P0139 HO2S Circuit Open (4.3L)
    P0171 Fuel Trim Lean (Lean Exhaust)
    P0172 Fuel Trim Rich (Rich Exhaust)
    P0320 Ignition Control Error (4.3L)
    P0321 Spark Reference Circuit
    P0327 Knock Sensor Circuit Grounded (4.3L)
    P0328 Knock Sensor Circuit Open (4.3L)
    P0342 Cam Signal Circuit
    P0400 EGR Error
    P0500 VSS Error (4.3L)
    P1222 Fuel Pump Voltage Low
    P1530 A/C Head Pressure Switch Circuit
    P1531 Low A/C Refrigerant Charge
    P1558 Cruise System Problem
    P1561 Cruise Vent Solenoid Circuit
    P1562 Cruise Vacuum Solenoid Circuit
    P1565 Cruise Servo Position Sensor Circuit
    P1567 Cruise Switches Circuit
    P1568 Cruise System Problem
    P1571 (1) Traction Control Torque Out Of Range
    P1573 (1) Traction Control Fault (Loss Of ABS/TCS Serial Data)
    P1599 Cruise Power Management
    P1623 PROM Error
    P1632 System Voltage High (4.3L)
    (1) Transmission code. For automatic transmission code diagnosis, see appropriate G - ELECTRONIC TRANSMISSION TESTS W/ CODES article in this section. See bullet list following this table.
  • G - TESTS W/CODES - ELECTRONIC TRANSMISSION (for Astro & Safari)
  • G - TESTS W/CODES - ELECTRONIC TRANSMISSION (for "S" & "T" Series)
  • G - TESTS W/CODES - ELECTRONIC TRANSMISSION (for "C" & "K" Series)
NOTE: Trouble code charts should only be used if Malfunction Indicator Light (MIL) is illuminated (indicating a current problem exists). Exceptions are Code 13, 15, 24, 44 and 45 charts, which may be used to help diagnose intermittent codes. Anytime Code 51, 52 or 55 is displayed with another code, start with 50-series code first and proceed to lower numbered codes.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.