MUT Hand Held Diagnostics & ECU Troubleshooting Codes

Engine Warning Lamp

The Engine Warning Lamp illuminates when the ECU detects one of the failure conditions in the code tables below, or when the ECU can no longer make proper adjustments to engine control.

Reading codes without a MUT unit

If a MUT hand-held tester is not available, codes can be read via lamp-flash count:

1. Locate the harness connector (see figure above).
2. Install a jumper wire (part MB991529) to PIN #1, with the other end attached to a proper ground (-).
3. Turn the ignition switch to ON. After a few seconds the Warning Lamp flashes the stored code(s). Example: Error Code #24 (Speed Sensor) flashes as 2 flashes, pause, 4 flashes (1.5 sec light-on / 0.5 sec light-off pulses, ~2 sec gap between digit groups, ~3 sec gap between repeats).
4. The code sequence repeats continuously until the ignition switch is returned to OFF.
5. After repairs, clear all memory codes by disconnecting the negative (-) battery cable for 30 seconds.
6. Restart the engine and warm to operating temperature. If the warning light no longer appears, the repair is confirmed.
7. If the warning light reappears, repeat the testing sequence.

Note: if no flashes are present at all, the ECU itself has failed and requires servicing.

Common Failure Codes

Code #	Problem Circuit
13	Intake Air Temperature Sensor (MAF)
14	Throttle Position Sensor (TPS)
21	Water Temperature Sensor
22	Crankshaft Position Sensor
24	Speed Sensor
31	Knock Sensor
32	Boost Sensor

(verify printed p.125) — the source table has separate “SOHC” / “DOHC” columns marking which codes apply to which engine, but the checkmark grid did not survive OCR (only a single stray circle/checkmark character was recoverable, next to the Knock Sensor / Boost Sensor rows — consistent with those two being DOHC-turbo-only, which matches known hardware, but not confirmed from the page itself). Do not assume the other five codes are shared across both engines without checking a clean scan.

Complete Code List

Code #	Problem Circuit
11	Oxygen Sensor
13	Intake Temperature Sensor
14	Throttle Position Sensor (TPS)
16	Battery Circuit Low Voltage
18	Starter Switch Circuit
21	Water Temperature Sensor
22	Crankshaft Position Sensor
26	Idle Switch (DOHC-Turbo)
27	Power Steering Pressure Switch
28	A/C Switch
29	Neutral Safety Switch
32	Boost Sensor
33	ECU Power ON Circuit Switch
41	Injector Circuit
44	Timing Circuit System
45	ISC Servo

This table’s 16 code/circuit pairs are a clean 1:1 OCR match (no ambiguity in row order) and are transcribed as printed on p.125-126.

(verify printed p.125-126) — codes 24 (Speed Sensor) and 31 (Knock Sensor), both listed in the Common Failure Codes table above, do not appear in this “Complete Code List” table, and codes 23, 25, 30, 34-40, 42-43 are also absent. This may mean the source page’s list genuinely isn’t exhaustive despite its heading, or that rows were lost in OCR/scan. Do not assume codes 24 and 31 are unsupported by the ECU — treat this list as printed-but-incomplete pending a clean re-scan.

See also: Engine ECU Connector Pin Guide, Diagnostic Harness Pin Guide.