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Understanding ALDL
(Assembly Line Data Link)

The ALDL (Assembly Line Data Link) is located under the dash of your SyTy, just below the steering column. It enables you to "pull codes" whenever your "CHECK ENGINE" light begins to flash. These codes alert you to certain engine components that are detecting a problem, such as, EST codes, low voltage to certain sensors, and high voltage to certain sensors (amongst many). To check codes and view data from the ALDL you can use a Scantool, many exist on the market today. All you really need is a paperclip.  Here's how to use the ALDL.

Using the above diagram, the ports are as follows:

A = Ground, B = Diagnostic Terminal, F = Torque Converter Clutch, 
G = Fuel Pump, H = Brake Sense Speed Input, M = Serial Data (Do Not Use)

Now, with the engine off and the ignition off, take a paperclip (or code scanner) and jumper ports A & B. This will read the engine diagnostic codes. Turn the ignition to the on position, but not the engine. The check engine light should begin showing some activity. Now, this is where you have to do some paying attention and writing. The check engine light will flash in numbered sequences to reveal the codes stored by the ECM. Here's how to decipher them:

  • The check engine light will flash a code 12 (1 flash....pause....2 flashes = 12) three times to let you know that you are in diagnostic testing. This is normal and does not signify an engine fault.
  • After the code 12 flashes three times, the check engine light will begin flashing engine codes three times if any are present. Pay close attention, so as not to miss the pauses.
  • When all the codes have flashed, the code 12 will cycle three more times to let you know that it is through. Turn off the ignition and remove the paperclip.
  • Disconnect the negative feed (black wire) from the battery to clear the codes. Leave it off for a few seconds and then reconnect it.

Now, you have a list of codes that you just pulled from your vehicle (hopefully not), but what do they mean?

ENGINE CODES

Trouble Codes Circuit or System Probable Cause

CODE 12

Diagnostic or no distributor reference pulses to ECM Explanation above, but if this code flashes while the vehicle is running, then then no reference pulses are reaching the ECM.
CODE 13 Oxygen Sensor Circuit Check for a sticking or misadjusted TPS. Check wiring to O2 Sensor. Replace O2 Sensor.
CODE 14 Coolant Sensor - High Temp Fix overheating problems, if any. Check all wiring to coolant sensor. Replace coolant sensor.
CODE 15 Coolant Sensor - Low Temp See above.
CODE 21 TPS Voltage High (Throttle Position Sensor) Check for sticking or misadjusted TPS plunger. Check all wiring between TPS and ECM. Adjust or replace TPS.
CODE 22 TPS Voltage Low (Throttle Position Sensor) See above.
CODE 23 MAT Low Temp Indication This code will set if the MAT sensor, it's connections, or it's wires are open for 3 seconds.
CODE 24 VSS (Vehicle Speed Sensor) A fault in this circuit should only be indicated when the vehicle is in motion. Disregard if it is indicated when sitting still. Check the connections at the ECM. Check the TPS setting.
CODE 25 ATI Sensor - High Air High Temp indication. Sets if the sensor or signal line becomes grounded for 3 seconds.
CODE 32 EGR Vacuum switch shortened to ground on start-up or switch not closed sfter ECM has commanded the EGR for a period of time. Replace valve. * If you disconnect the EGR and run the Ultimate on T1-15 it may set this code.
CODE 33 MAP Sensor Check the vacuum hoses from the MAP sensor. Check the wiring at the ECM. Replace the MAP sensor.
CODE 34 Vacuum Sensor or MAP Sensor This will set when the signal voltage from the MAP sensor is too low. Instead the ECM will substitute a fixed MAP value and use the TPS to control fueling. Replace MAP sensor.
CODE 35 IAC Valve (Idle Air Control) Code will set when closed throttle speed is 50 rpm above or below the correct idle speed for 30 seconds. Replace the IAC.
CODE 42 EST (Electronic Spark Timing) The code is set when this circuit is grounded or open. A malfunctioning HEI module can cause this code.
CODE 43 ESC (Electronic Spark Control) The ESC retard signal has been on for too long or the system has failed a functional check.
CODE 44 O2 - Lean Exhaust Check the ECM wiring connections, particularly terminals 8 & 15. Check for vacuum leakage at the TB base gasket, vacuum hoses, or the intake manifold gasket. Replace the O2 Sensor.
CODE 45 O2 - Rich Exhaust Check the evaporative charcoal canister and it's components for the presence of fuel. Replace the O2 Sensor.
CODE 51 PROM or MEM-CAL Make sure the PROM or MEM-CAL is properly seated in the ECM. Replace the PROM or MEM-CAL.
CODE 52 CALPAK Check the CAL-PAK to ensure proper installation. Replace the CAL-PAK.
CODE 53 System Over-Voltage Indicates a basic alternator problem. Check charging system.
CODE 54 Fuel Pump Low Fuel Pump voltage. Sets when the fuel pump voltage is less than 2 volts when reference pulses are being received.
CODE 55 ECM Be sure that the ECM ground connections are tight. If they are, replace the ECM.

Now, all of a sudden your brake lights decide to come on and stay on. What's the deal with that? Well, the ECU can also store codes from the 4 wheel anti-lock system (4WAL). To read these codes, do the same thing as engine codes, except jumper A & H terminals. To remove brake codes from the ECU, jumper A & H for 2 seconds, remove for 1 second, and replace for 2 seconds. The Antilock/Brake light should light, then go off.

4WAL DIAGNOSTIC CODES

Trouble Codes Circuit or System Probable Cause

CODE 21

Right Front Wheel Circuit Faulty wheel sensor or open circuit.
CODE 22 Right Front Wheel Circuit No signal. Remove the wheel. Check for a damaged sensor or loose electrical connectors.
CODE 23 Right Front Wheel Circuit Intermittent signal, indicating a loose electrical connector.
CODE 25 Left Front Wheel Circuit No signal. Remove the wheel. Check for a damaged sensor or loose electrical connectors.
CODE 26 Left Front Wheel Circuit Intermittent signal, indicating a loose electrical connector.
CODE 27 Left Front Speed Sensor Circuit Faulty sensor or loose elctrical connector.
CODE 28 Speed Sensor Signal Erratic brake action at low speeds and pedal pressure is a sign of a fault in the speed sensor unit or speedometer.
CODE 29 EHCU Circuit A loss of signal from all 4 sensors indicates a loose EHCU connector.
CODE 31 Right Rear Speed Sensor Circuit An intermittent code indicates a loose electrical connector.
CODE 32 Right Rear Wheel Circuit No signal. Remove the wheel. Check for a damaged sensor or loose electrical connectors.
CODE 33 Right Rear Wheel Circuit Intermittent signal, indicating a loose electrical connector.
CODE 35 Left Rear Wheel Circuit Intermittent signal, indicating a loose electrical connector.
CODE 36 Left Rear Speed Sensor Circuit No signal. Remove the wheel. Check for a damaged sensor or loose electrical connectors.
CODE 37 Left Rear Speed Sensor Circuit An inconsistent anti-lock action at low speeds and pedal pressure is a sign of a fault in the speed sensor unit or connectors.
CODE 38 EHCU Valve Circuit A pulsing pedal indicates a defective wheel sensor or faulty EHCU valve.
CODE 41 thru 66 4WAL Control Unit or Motor Circuit Check for a loose ground connection at the motor circuit. Clear the codes and drive the vehicle. If any of these codes return, the EHCU valve may be faulty.
CODE 67 Motor Circuit Check the motor for loose electrical connections.
CODE 68 Motor Circuit A locked motor or an open circuit. Check the wiring for the motor.
CODE 71 thru 74 4WAL Control Unit Clear the codes and drive the vehicle. If any of these codes return, the EHCU valve may be faulty.
CODE 81 Brake Switch Circuit Make sure the driver hasn't been riding the brake. Check the brake switch adjustment and electrical connections.
CODE 86 Anti-Lock Warning Light Check the light and wiring for a short cicuit.
CODE 88 Brake Warning Light Check the light and wiring for a short cicuit.

 

OTHER ALDL CAPABILITIES

To engage the TCC - jumper A & F - This will engage the transmission converter clutch. This is used by racers at the track to engage a mechanically link between the TC and the tranny, thus reducing slippage throughout the run. Has been found to provide better performance, but not recommended for daily use.

To engage the Fuel Pump - connect a fused (+) lead to terminal G - This will cut the fuel pump on. This is a good thing to do when checking out a SyTy for purchase, since you need to check the codes anyway. This verifies that the pump is in working order.