On the 1990 to 1992 year cars, the tps has two separate sensors in one housing, one does the engine, the other does the transmission. After 1992, one sensor talks to both the engine and trans. On the early cars, to about 1993, the sensor is under the throttle and is turned by the throttle shaft.
Various year cars had different idle voltage settings :
87-88 .24 - .40
89-90 .31 - .36
90 and up .57 - .62
Full throttle should read about 4.5 volts.
Be careful to prevent anything getting in the tps while cleaning the throttle out...don't spray any cleaners in the throttle or the gunk will wash into the sensor.
12.18 - Fuel Fail 18 : Throttle Position Sensor and maf Sensor by Brett Gazdzinsky
High throttle position signal, low air flow signal : the ECU looks for a combination of high throttle signal and low air flow signal that can not occur in a normally operating system.
Conditions for flagging :
- Throttle position sensor 2.25 volts or greater,
- Engine load site 3 or lower (low maf sensor output)
Response time : 5 engine revolutions.
Default settings: ignore throttle position sensor.
Possible faults:
- High resistance connection to ECU or throttle position sensor,
- Restricted air intake,
- Restricted exhaust,
- Low fuel pressure (low engine power)
- Ignition fault (low engine power)
- Engine mechanical fault,
- Short or open circuit between ECU and maf sensor,
- Incorrectly adjusted throttle position sensor,
- Bad throttle position sensor,
- bad maf sensor.
Check tps output signal, maf sensor output signal, engine vacuum readings.
12.19 - Fuel Fail 19 : Low Throttle Position Sensor by Brett Gazdzinsky
High air flow signa, the ECM sees a combination of closed throttle and high intake airflow signals.
Conditions for flagging FF19:
- Throttle position sensor at idle,
- Engine load site 13 or higher,
- Engine rpm,s 1000 or higher for 5 or more crankshaft revolutions.
Default with FF19 flagged: ecu ignores throttle sensor and sets 1.5 volts, idle functions are disabled.
Possible faults:
- High resistance connection to ecu, maf sensor or throttle position sensor.
- Water in MAF sensor,
- Short or open in maf and throttle sensor wiring,
- Bad throttle position sensor.
Clean and wd40 the connections to the tps and maf sensors. Measure the throttle position sensor resistance at idle and as you open the throttle.
12.22 - Fuel Fail 22 fuel pump control circuit by Brett Gazdzinsky
ECU flags FF22 if the signal to the fuel pump relay indicates open or shorted.
Conditions for flagging FF22:
- Ignition on,
- Fuel pump operating,
- indications of open or shorted fuel pump relay coil circuit.
- Response time 600 milliseconds
Possible faults:
- Low battery voltage,
- Poor ecu power feed or ground connections,
- Short or open circuit between ecu and fuel pump relay,
- Short or open circuit to oxy sensor heater relay (1993 and up),
- Loose connector pins (li18) 6 way PM4 yellow connector under air cleaner (1991-1992)
- Bad relay,
- Air pump relay circuit fault.
If the fuel pump does not work, but FF22 is NOT flagged, its the relay (contacts), the connections at the fuel pump, or a bad fuel pump.
12.26 - Fuel Fail 26 oxy sensor feedback out of range, lean by Brett Gazdzinsky
Fuel fail 26 is . As the engine gets partly warmed up, it stumbles and sets the code. The code will clear when the trouble does, on the next restart.
Possible faults for a FF26 are :
- Low fuel pressure (plugged filter, weak pressure regulator on fuel rail, plugged system)
- Intake manifold air leak (vacuum hoses, intake manifold gasket, evap system hose rot, egr pipe rusted out, problem with air injection system (leaking valve).
- Ignition misfire, (bad plug, wires, cap, rotor)
- Purge valve stuck open (vacuum leak in evap system)
- Oxy sensor fault (not common)
- Bad maf sensor or connections.
Best to start with the ignition system : If the wires, cap, rotor are old, replace them, along with spark plugs.
The catalytic converters may eventually melt plugging the exhaust if the car is ran with the FF alarm on, so don't ignore it just because the engine runs ok.
12.39 - Fuel Fail 39, EGR temp sensor circuit by Brett Gazdzinsky
The ECM looks for a low egr temp signal when the egr valve is closed, and a high temp signal when the egr valve is open. The ECM also looks for an over temp signal when the egr system is enabled.
The egr temp sensor is located behind the throttle in the bottom of the intake manifold, close to the exhaust gas entry point.
The egr temp sensor is a negative temp coefficient thermistor :
Resistance decreases with temp increase.
Resistance, 122f 560,000 to 710,000 ohms.
Resistance, 212F 76,000 to 94,000 ohms.
Conditions for flagging FF39 :
- Engine coolant temp above 180F,
- Throttle position within expected range for engine speed,
- Engine speed 1700 to 3000 rpm,s,
- Load site range 2 to 7,
- Egr enabled, indicated temp greater than 525F for 64 milliseconds,
- EGR enabled, indicated temp under 212F for 60 seconds,
- EGR disabled, indicated temp greater than 122F for 5 minutes.
Possible faults:
- Blockage in EGR transfer pipe between egr valve and intake manifold,
- Blockage in intake manifold EGR adaptor port (90% of problems),
- Disconnected, leaking, blocked, pinched vacuum hose between,
- EGR valve and the egr vacuum solenoid,
- Defective EGR solenoid valve (stuck),
- Defective EGR valve,
- Defective egr temp sensor,
- Open or short in egr temp sensor wiring.
Most modern cars use exhaust gas into the intake tract to reduce combustion temps and NOx because exhaust gas is inert. It has no fuel or oxygen.
The EGR system ONLY operates when the engine is up to temperature and the engine is under light or moderate loads.
12.44 - Code 44
The code 44 and 26 have some overlap. Code 44 means that the oxygen sensor is signaling the computer that the fuel mixture is bad - too rich or too lean. The car can then not run in closed loop mode, and the VCM after a while ignores the oxygen sensor and goes to a default mode. If the sensor itself was bad, the car would probably run just fine, but use more gas, although in some cases will run irregularly. More likely you have a true, too lean or too rich problem.
The first step in diagnosis is to idle the car until the car runs rough or the error light is activated. Then, using a DIGITAL multimeter, measure the output of the oxygen sensor by back probing it while still connected - do this at the junction of the wire from the sensor on the right (US) fender well. It will oscillate rapidly under normal conditions from .9 to 2v. If mixture is too lean it will read very low all the time. Check with a manual for the actual voltages, these may be incorrect, or vary between models.
TOO LEAN: If you determine that the mixture is too lean, then you have either fuel starvation or an intake air leak. If the car idles OK but has loss of power at speed, then you likely have fuel starvation. An intake air leak will cause bad idle but will be less noticeable at speed.
TOO RICH OR AMBIGUOUS: This could be a sensor problem (air mass sensor, throttle pot or others), but most likely an ignition problem. This may well be the most common cause for code 44. Before you do anything you check the ignition, try just replacing distributor cap and rotor , spark plug wires, and spark plugs. - Its cheap and easy and maintenance anyway. It might be possible that a misfire resulted in fouling of the oxygen sensor (code 26), then when replaced with a new one you got code 44.
Conditions for flagging...
- Engine coolant temp above 167F,
- Throttle position under 3 volts,
- 450 engine revolutions in a row no oxy sensor switching.
Possible faults:
- Fuel pressure fault,
- Stuck open purge valve,
- Poor ground connections,
- Poor oxy sensor ground connection,
- Open or short in oxy sensor heater and/or output circuit,
- Defective air injection pump or circuit,
- Intake air leak,
- Plugged fuel injector (or bad electrical connection)
- Defective maf sensor.
Do a hot engine vacuum reading. At about sea level, you should get roughly 20 inches of vacuum at hot idle.
You can have a vacuum leak in many impossible to see places....
- The egr system/pipes/valve,
- The vapor recovery system...at the vacuum port under the throttle (nipple falls out of manifold), at the charcoal canister hoses in the front air dam, intake manifold,
- Crankcase vent system, etc.
After that, check the fuel pressure and the injectors. You can unbolt the rail from the intake manifold and remove it, then remove each injector and check the intake screens. At that time, you can also remove the fuel pressure regulator and using air pressure, test the pressure set point. Should be 44 psi without any vacuum on the vacuum port. Fuel pressure typically runs between 32 to 44 psi, 44 psi full throttle (no vacuum), 32 psi with 20 inches of vacuum...
Ignition problems typically set a ff26. During a severe miss, fuel and air is dumped into the exhaust, setting the FF26. For FF44, the engine seems to not be able to get enough gas into the mixture. This means a shortage of fuel, or an abundance of air.
When heated with a torch till its hot and slightly glowing, the oxy sensor should put out about .9 volts. Voltage reading will vary around as you move the torch, but if it gets up to .9 volts, its ok.
I doubt they fail often, typically when the heater gets erratic. They have to be hot to work, so if they don't get hot, they don't work. The relay that powers the heater also runs the fuel pump.
You could have a big vacuum leak when the ecu operates the canister purge. The ecu will open the solenoid to purge the fuel vapors in the canister
after the engine is up to at least 93F and above idle.
12.48 Fuel Fail 48 : Idle Speed Control Valve - Stepper motor grossly out of position by Brett Gazdzinsky
The idle speed control valve adjusts the idle speed, something abnormal going on with the idle speed will be a sympton of problem as the ECM looks for the ISCV far out of position at idle.
Conditions for flagging ...
Throttle position...at idle
Engine coolant temp above 186F
ISCV full open
Engine speed lower than normal.
Or,
Engine coolant temp less than 94F
ISCV full closed,
Engine speed greater than normal.
Possible faults...
- Low battery voltage,
- Loss of ECM memory power,
- Loss of ECM ground connection,
- Badly mis adjusted idle bypass screw,
- Badly mis adjusted throttle,
- Air leak past ISCV,
- Low engine power at idle when hot,
- Stuck ISCV,
- Blocked ISCV port or hose.
The idle speed control valve adjusts the idle speed from a base idle speed, both up and down. Say the base idle speed is set for 500 rpm before the ISCV adjusts it...it can move the idle down 30 steps, and up 200 steps.
The ecu learns the correct default position and stores it if you start the engine cold, let it warm up fully without stepping on the gas, then drive off.
If the throttle is messed with, or the engine has a big vacuum leak, the ISCV will be at the end of its adjustment, or not be able to get the idle speed low enough, and set codes.
Many times, people who don't know fuel injection cars try to adjust the idle speed at the throttle. This will do nothing but cause problems till the ISCV runs out of adjustment, then the idle speed will start changing.
I would guess you just have to have the idle speed set up, or a vacuum leak fixed and all will be well.
12.89 - Fuel code 89
Purge valve. See Purge Valve
