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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.