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Diagnostics 2 - Engine Code Breaking

OBD-I Troubleshooting & Engine Code Breaking

Apr 1, 2003
0304_turp_02_z+diagnostics+engine_code_scanners Photo 1/8   |   Diagnostics 2 - Engine Code Breaking

In the last Diagnostics episode, we outlined the vital information provided by compression and leakdown testing and illustrated how to use these most important tools. These tests reveal the internal health of the engine and are key when purchasing a used car, whether it be for a project or strictly as a driver, not to mention tracking the fitness of a typical high-mileage commuter.

We wanted to take a different approach here and decided to look at troubleshooting challenges from an electronic standpoint. We will look at tools that will help you determine why the engine won't start, decipher what is causing the famed "check engine" light, and track down electrical gremlins.

Turp_0304_13_z+diagnostics+sunpro_kit Photo 2/8   |   This Sun Pro kit, available from JC Whitney (13ZH6156R), has everything the OBD-I owner needs to recall engine codes and test out the sensor or component said code identifies.

The cool thing is we found it all in one package. Thumbing through the JC Whitney catalog we saw the perfect troubleshooting kit that addresses the concerns of beginners but provides the capability to tackle complex problems.

It should be noted that this article will focus on OBD-I controlled vehicles. The transition to OBD-II was initiated in 1995-6 models and the year of transition differed from manufacturer to manufacturer and even from model to model.

The Kit
The Sunpro Master Technician's Kit (13ZH6156R) contains six diagnosis scanner/testers, detailed instruction manuals and two videos to help beginners get a handle on the tools.

There are three different computer code readers: one for GM, one for Ford and an import scanner that covers Toyota, Nissan and Honda. There is a sensor tester for engine sensors and ignition modules and a sensor probe that tests MAF, MAP and VAP sensors. Lastly is a seven-channel Multimeter-the bloodhound of diagnostics tools that sniffs out electrical gremlins.

The kit is a great investment for the enthusiast, and with its wide range of applications, car clubs would also be wise to consider investing in the Sunpro setup. The introduction videos bridge the gap between the pages of the manuals and the actual underhood of the car by visualizing the location and look of connectors and providing a better hands-on understanding of what it takes to draw the error codes from the ECU.

Turp_0304_09_z+diagnostics+ecu_switch Photo 3/8   |   Nissan computer: On popular Nissans of the mid-'90s, it all happens right on the ECU. First mark the original position of the Diagnosis Mode Selector then turn the adjuster fully clockwise and after a three-second pause full counterclockwise. A flashing red LED in the code window on the ECU indicates it is in diagnostic mode. The LED will then flash the codes, which are all two digits in length.

Code Breaking
Harvesting the codes requires different approaches for different makes.

For Toyotas you will either plug in a code scanner or use the supplied jumper wire to facilitate code gathering. A rectangular multi-pin connector requires the scan tool and circular two-pin connector means it's time to break out the jumper wire.

Testing is done with the key in the On position, and the codes are read on the dash in the form of flashes of the check engine icon light.

On pre-1989 ECUs, the codes are flashed in a single burst with either a three- or 4.5-second delay between codes. So a code 12 would be 12 flashes in succession.

Cars from 1989 and up have no single-digit codes and all codes flash one digit at a time with a pause between digits. A code 12 here would be a single flash followed by a pause then two quick flashes.

Turp_0304_07_z+diagnostics+voltmeter Photo 4/8   |   The Sunpro CP 7678 Multimeter reads DC volts, resistance, current draw and has high tech and low tack scales as well as dwell in degrees and duty cycle in percentage. It can be used to check the health of the electrical system and confirm if switches, solenoids and relays are functioning properly. The unit's manual shows you how it's done.

Nissan has a different approach altogether. The kit outlines code retrieval for 1984 to 1992 models. Most of the popular models use a selector tool to access the codes at the ECU. The selector is a plastic screwdriver that inserts into the Diagnosis Mode Selector, which is a potentiometer, to switch the ECU to diagnostics mode.

Before making the switch you must mark where the potentiometer is set at so you can put the computer back into its original position and have the key in the On position.

The Mode Selector is turned fully clockwise and, after a three-second pause, full counterclockwise. A flashing red LED in the code window on the ECU indicates it is in diagnostic mode. The LED will then flash the codes, which are all two digits in length.

Turp_0304_03_z+diagnostics+import_scanner Photo 5/8   |   The import code talker is used to retrieve engine codes from OBD-I Toyotas, Nissans and Hondas. The kit also includes code scanners for OBD-I Ford and GM vehicles.

This kit covers 1985 to 1992 Hondas and during these years the Honda ECUs went through some major revisions. The early ECUs had four LEDs. Each LED had a different value (1, 2, 4, 8). If the Check Engine light came on, the computer displayed the code without requiring a switch over to a diagnostics mode.

All you do is observe the LEDs and add up the values of the lights. So the number 2 LED on means code 2. The number 4 and 2 illuminated means code 6 and so on. Later ECUs flash in short and long duration bursts. Short bursts for single digit while a long burst is the first digit of a two-digit code. Some 1991 and all 1992 and up ECUs use a jumper wire to initiate code reading and use the short/long flash method.

It should be noted that all codes must be erased after repairs and the manual details these procedures for each make.

Turp_0304_04_z+diagnostics+map_and_maf_sensor_tester Photo 6/8   |   The Sensor Probe is used to identify problems in MAP, MAF or Vein Airflow sensors.

Deciphering The Code
Breaking the code is only part of the battle. Deciphering the meaning of the numbers you have retrieved will allow you to pinpoint the problem area. The manual breaks down the codes and gives an insight into what may be wrong.

We have listed baseline codes in the accompanying chart for imports only because there are dozens of ECU and transmission codes for Ford and GM products and not enough room here to even come close to providing an overview of the pertinent number groups.

Component Diagnosis
Diagnosing is a chase wherein you box in the problem by eliminating possibilities and pinpointing the component that is faulty.

Turp_0304_06_z+diagnostics+sensor_tester Photo 7/8   |   The included Sensor Tester is used to check codes that lead to the TPS, EGR, O2, Temperature, Knock and Hall Effect sensors as well as ignition modules.

The included Sensor Tester is used to check codes that lead to the TPS, EGR, O2, Temperature, Knock and Hall Effect sensors as well as ignition modules. The Sensor Probe is used to identify problems in MAP, MAF or Vein Airflow sensors.

The Multimeter reads DC volts, resistance, and current draw and has high tech and low tack scales as well as dwell in degrees and duty cycle in percentage. It can be used to check the health of the electrical system, confirm if switches, solenoids and relays are functioning properly. It can verify that ignition coils and wires, fuel injectors and a number of other sensors are in working order.

If you are rolling an OBD-I-equipped car this kit hits the bull's-eye. While we cover the basics here, we cannot rave enough about the info in the manuals and on the videos; it puts forth the proper information in an easy-to-understand manner. The kit gives enthusiasts the Sherlock Holmes intuition needed to narrow down the suspects and flush out the guilty party when it comes to the smooth running of their car. Next time our Diagnostics section will address the code breaking needs of OBD-II cars.

Turp_0304_12_z+diagnostics+sunpro_troubleshooting_chart Photo 8/8   |   Diagnostics 2 - Engine Code Breaking

Code Breaking Tech(Codes address different sensors depending on year and model)

Toyota CCS 1989-up
Code Translation
11 ECU Power Supply
12 RPM Signal
13 RPM Signal
14 Ignition Signal
15 ECT System
21 Main O2 Sensor
22 Coolant Temp Sensor
23 TPS Signal
24 Intake Air Temp Sensor
25 Lean Air/Fuel Mixture
26 Rich Air/Fuel Mixture
27 O2 Sensor
28 Main O2 Sensor
31 Vacuum Sensor Signal
32 Airflow Meter Signal
34 Turbocharger Pressure Signal
35 Turbocharger Pressure Signal/High
  Altitude Compensator
41 THP Sensor
42 Vehicle Speed Sensor
43 Starter Signal
51 Switch Condition
52 Knock Sensor Signal
53 Knock Sensor Control
54 Intercooler ECU Signal
55 Knock Sensor
71 EGR System
72 Fuel Cut Solenoid

{{{Honda}}} 1985-1992
Code Translation
1 O2 Sensor/Pressure Regulator
2 O2 Sensor/Vehicle Speed Sensor/ECU
3 MAP Sensor
4 TDC Crank Sensor/Crank Angle
  Sensor/Pulse Generator/Vacuum
5 MAP Sensor
6 Coolant Temp Sensor
7 TPS Sensor/Clutch Switch({{{M}}}-T)/Shift
  Position Signal (A-T)
8 TDC Sensor/Pulse Generator/Ignition
  Output/CYL Sensor/Crank
  Angle Sensor
9 Cylinder #1 Sensor/TDC Sensor/Pulse
  Generator/Ignition Output/CYL
  Sensor/ Crank Angle Sensor
10 Intake Air Temp Sensor
11 Idle Mixture Adjuster
12 EGR System
13 Atmospheric Pressure Sensor
14 Electronic Air Control Valve/Idle
  Control System/ECU
15 Ignition Output Signal/ECU
16 Fuel Injector Circuit
17 Vehicle Speed Sensor
19 Lock-up Control Solenoid
20 Electrical Load Detector
21 VTEC Spool Valve
22 VTEC Oil Pressure Switch
23 Knock Sensor
30 Automatic Trans “A” Signal
31 Automatic Trans “B” Signal
41 O2 Sensor Heater/Linear
  Air-Fuel Ratio
43 Fuel Supply System
48 Linear Air-Fuel Ratio
Code Translation
11 Crank Angle Sensor
12 Mass Airflow Sensor
13 Coolant Temp Sensor
14 Vehicle Speed Sensor
21 No Ignition Reference/Ignition System
22 Fuel Pump/Idle Speed Control
23 Idle Switch/Throttle Valve Switch
24 Idle Switch/Transmission
  Switch/Neutral-Park Switch
25 Idle Speed Control
31 ECU/Air Conditioning/Fan
  Switch/Power Steering Switch
32 EGR
33 O2 Sensor
34 Knock Sensor
35 EGR Temp Sensor
41 Air Temp Sensor
42 Fuel Temp Sensor/Throttle Sensor
43 TPS/Fuel Injector
45 Injector Leak
51 Fuel Injector(s) Electrical
53 O2 Sensor
54 Automatic Trans Signal
55 No Malfunctions Recorded


J.C. Whitney



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